The Abbasid Revolution, also called the Movement of the Men of the Black Raiment, was the overthrow of the Umayyad Caliphate (661–750 CE), the second of the four major Caliphates in early Islamic history, by the third, the Abbasid Caliphate (750–1517 CE). Coming to power three decades after the death of the Islamic prophet Muhammad and immediately after the Rashidun Caliphate, the Umayyads were an Arab empire ruling over a population which was overwhelmingly non-Arab. Non-Arabs were treated as second-class citizens regardless of whether or not they converted to Islam, and this discontent cutting across faiths and ethnicities ultimately led to the Umayyads' overthrow.

The Abbasid family claimed to have descended from al-Abbas, an uncle of Muhammad. The revolution essentially marked the end of the Arab empire and the beginning of a more inclusive, multiethnic state in the Middle East. Remembered as one of the most well-organized revolutions during its period in history, it reoriented the focus of the Muslim world to the east.

The Battle of the Zab (Arabic: معركة الزاب), also referred to in scholarly contexts as Battle of the Great Zāb River, took place on January 25, 750, on the banks of the Great Zab River in what is now the modern country of Iraq. It spelled the end of the Umayyad Caliphate and the rise of the Abbasids, a dynasty that would last from 750 to 1258 which is divided in to two periods: Early Abbasid period (750–940) and Later Abbasid period (940–1258).

The Battle of Talas or Battle of Artlakh was a military encounter and engagement between the Arab civilization and the Chinese civilization in the 8th century, specifically between Abbasid Caliphate along with its ally, the Tibetan Empire, against the Chinese Tang dynasty. In July 751 AD, Tang and Abbasid forces met in the valley of the Talas River to vie for control over the Syr Darya region of central Asia.

According to Chinese sources, after several days of stalemate, the Karluk Turks, originally allied to the Tang Dynasty, defected to the Abbasid Arabs and tipped the balance of power, resulting in a Tang rout. The defeat marked the end of the Tang westward expansion and resulted in Muslim Arab control of Transoxiana for the next 400 years.

Control of the region was economically beneficial for the Abbasids because it was on the Silk Road. Chinese prisoners captured in the aftermath of the battle are said to have brought paper-making technology to West Asia.

Abu Ja'far Abdallah ibn Muhammad al-Mansur usually known simply as by his laqab Al-Mansur (المنصور) was the second Abbasid caliph, reigning from 754 CE – 775 CE and succeeding As-Saffah. He is known for founding the 'Round City' of Madinat al-Salam, which was to become the core of imperial Baghdad.

Modern historians regard Al-Mansur as the real founder of the Abbasid Caliphate, one of the largest polities in world history, for his role in stabilizing and institutionalizing the dynasty.

Abd al-Rahman I, a prince of the deposed Umayyad royal family, refused to recognize the authority of the Abbasid Caliphate and became an independent emir of Córdoba. He had been on the run for six years after the Umayyads had lost the position of caliph in Damascus in 750 to the Abbasids. Intent on regaining a position of power, he defeated the existing Muslim rulers of the area who had defied Umayyad rule and united various local fiefdoms into an emirate. However, this first unification of al-Andalus under Abd al-Rahman still took more than twenty-five years to complete (Toledo, Zaragoza, Pamplona, Barcelona).

The Caliph al-Mansur founded the epicenter of the empire, Baghdad, in 762 CE, as a means of disassociating his dynasty from that of the preceding Umayyads (centered at Damascus) and the rebellious cities of Kufa and Basrah.

Thousands of architects, engineers, legal experts, surveyors, carpenters, blacksmiths, diggers, and ordinary laborers from across the Abbasid empire were brought in to survey, measure and excavate the foundations. Ya'qubi, in his Book of Countries,reckoned there were 100,000 workers involved. "They say that no other round city is known in all the regions of the world," according to Al-Khatib al-Baghdadi. Four equidistant gates pierced the outer walls where straight roads led to the centre of the city. The Kufa Gate to the south-west and the Basra Gate to the south-east both opened on to the Sarat canal – a key part of the network of waterways that drained the waters of the Euphrates into the Tigris. The Sham (Syrian) Gate to the north-west led to the main road on to Anbar, and across the desert wastes to Syria. To the north-east the Khorasan Gate lay close to the Tigris, leading to the bridge of boats across it.

The noble Iranian family Barmakids, who were instrumental in building Baghdad, introduced the world's first recorded paper mill in the city

Harun al-Rashid was the fifth Abbasid Caliph. His epithet "al-Rashid" translates to "the Orthodox", "the Just", "the Upright", or "the Rightly-Guided". He ruled from 786 to 809, traditionally regarded to be the beginning of the Islamic Golden Age.

Harun established the legendary library Bayt al-Hikma ("House of Wisdom") in Baghdad in present-day Iraq, and during his rule Baghdad began to flourish as a world center of knowledge, culture and trade. During his rule, the family of Barmakids, which played a deciding role in establishing the Abbasid Caliphate, declined gradually.

In 796, he moved his court and government to Raqqa in present-day Syria. A Frankish mission came to offer Harun friendship in 799. Harun sent various presents with the emissaries on their return to Charlemagne's court, including a clock that Charlemagne and his retinue deemed to be a conjuration because of the sounds it emanated and the tricks it displayed every time an hour ticked. Portions of the fictional One Thousand and One Nights are set in Harun's court and some of its stories involve Harun himself.

On Zubaidah bint Ja`far ibn Mansur fifth pilgrimage to Mecca, she saw that a drought had devastated the population and reduced the Zamzam Well to a trickle of water. She ordered the well to be deepened and spent over 2 million dinars improving the water supply of Makkah and the surrounding province. "This included the construction of an aqueduct from the spring of Hunayn, 95 kilometers to the east, as well as the famed "Spring of Zubayda" on the plain of Arafat, one of the ritual locations on the Hajj. When her engineers cautioned her about the expense, never mind the technical difficulties, she replied that she was determined to carry out the work "were every stroke of a pickax to cost a dinar", according to Ibn Khallikan. "

She also improved the pilgrim route across nine hundred miles of desert between Kufa and Mecca. The road was paved and cleared of boulders and she assembled water storages at intervals. The water tanks also caught the surplus rainwater from storms that occasionally drowned people.

In 800, the Abbasid Caliph Harun al-Rashid appointed Ibrahim I ibn al-Aghlab, son of a Khurasanian Arab commander from the Banu Tamim tribe, as hereditary Emir of Ifriqiya as a response to the anarchy that had reigned in that province following the fall of the Muhallabids. At that time there were perhaps 100,000 Arabs living in Ifriqiya, although the Berbers still constituted the great majority.

Ibrahim was to control an area that encompassed eastern Algeria, Tunisia and Tripolitania. Although independent in all but name, his dynasty never ceased to recognise Abbasid overlordship. The Aghlabids paid an annual tribute to the Abbasid Caliph and their suzerainty was referenced in the khutba at Friday prayers.

It appears that Tibetans captured a number of Caliphate troops and pressed them into service on the eastern frontier in 801. Tibetans were active as far west as Samarkand and Kabul. Abbasid forces began to gain the upper hand, and the Tibetan governor of Kabul submitted to the Caliphate and became a Muslim about 812 or 815. The Caliphate then struck east from Kashmir but were held off by the Tibetans.

The Barmakid family was an early supporter of the Abbasid revolt against the Umayyads and of As-Saffah. This gave Khalid bin Barmak considerable influence, and his son Yahya ibn Khalid (d. 806) was the vizier of the caliph al-Mahdi (ruled 775–785) and tutor of Harun al-Rashid (ruled 786–809). Yahya's sons al-Fadl and Ja'far (767–803), both occupied high offices under Harun.

Many Barmakids were patrons of the sciences, which greatly helped the propagation of Iranian science and scholarship into the Islamic world of Baghdad and beyond. They patronized scholars such as Gebir and Jabril ibn Bukhtishu. They are also credited with the establishment of the first paper mill in Baghdad. The power of the Barmakids in those times is reflected in The Book of One Thousand and One Nights the vizier Ja'far appears in several stories, as well as a tale that gave rise to the expression "Barmecide feast".

In 803, the family lost favor in the eyes of Harun al-Rashīd, and many of its members were imprisoned.

The Battle of Krasos was a battle in the Arab–Byzantine Wars that took place in August 804, between the Byzantines under Emperor Nikephoros I (r. 802–811) and an Abbasid army under Ibrahim ibn Jibril. Nikephoros' accession in 802 resulted in a resumption of warfare between Byzantium and the Abbasid Caliphate. In late summer 804, the Abbasids had invaded Byzantine Asia Minor for one of their customary raids, and Nikephoros set out to meet them. He was surprised, however, at Krasos and heavily defeated, barely escaping with his own life. A truce and prisoner exchange were afterwards arranged. Despite his defeat, and a massive Abbasid invasion the next year, Nikephoros persevered until troubles in the eastern provinces of the Caliphate forced the Abbasids to conclude a peace.

A school of medicine is established in Baghdad by Harun al-Rashid and his vizier, Yahya ibn Khalid.

A major revolt led by Rafi ibn al-Layth was started in Samarqand which forced Harun al-Rashid to move to Khorasan. Harun al-Rashid became ill and died very soon.

After Rashid's death, the empire was split by a civil war between the caliph al-Amin and his brother al-Ma'mun, who had the support of Khorasan. This war ended with a two-year siege of Baghdad and the eventual death of Al-Amin in 813. Al-Ma'mun ruled for 20 years of relative calm interspersed with a rebellion in Azerbaijan by the Khurramites, which was supported by the Byzantines. Al-Ma'mun was also responsible for the creation of an autonomous Khorasan, and the continued repulsing of Byzantine forays.

This Battle of Rayy (one among many) was fought on May 1, 811 AD as part of an Abbasid civil war (the "Fourth Fitna") between the two half-brothers, al-Amin and al-Ma'mun.

Abu al-Abbas Abdallah ibn Harun al-Rashid, better known by his regnal name Al-Ma'mun, was the seventh Abbasid caliph, who reigned from 813 until his death in 833. He succeeded his half-brother al-Amin after a civil war, during which the cohesion of the Abbasid Caliphate was weakened by rebellions and the rise of local strongmen much of his domestic reign was consumed in pacification campaigns. Well educated and with a considerable interest in scholarship, al-Ma'mun promoted the Translation Movement, the flowering of learning and the sciences in Baghdad, and the publishing of al-Khwarizmi's book now known as "Algebra". He is also known for supporting the doctrine of Mu'tazilism and for imprisoning Imam Ahmad ibn Hanbal, the rise of religious persecution (mihna), and for the resumption of large-scale warfare with the Byzantine Empire.

Algebra was significantly developed by Persian scientist Muhammad ibn Mūsā al-Khwārizmī during this time in his landmark text, Kitab al-Jabr wa-l-Muqabala, from which the term algebra is derived. On the Calculation with Hindu Numerals, written about 820, was principally responsible for spreading the Hindu–Arabic numeral system throughout the Middle East and Europe.

The Muslim conquest of Sicily began in June 827 and lasted until 902, when the last major Byzantine stronghold on the island, Taormina, fell. Isolated fortresses remained in Byzantine hands until 965, but the island was henceforth under Muslim rule until conquered in turn by the Normans in the 11th century. Although Sicily had been raided by the Muslims since the mid-7th century, these raids did not threaten Byzantine control over the island, which remained a largely peaceful backwater. The opportunity for the Aghlabid emirs of Ifriqiya came in 827, when the commander of the island's fleet, Euphemius, rose in revolt against the Byzantine Emperor Michael II. Defeated by loyalist forces and driven from the island, Euphemius sought the aid of the Aghlabids. The latter regarded this as an opportunity for expansion and for diverting the energies of their own fractious military establishment and alleviating the criticism of the Islamic scholars by championing jihad, and dispatched an army to aid him. Following the Arab landing on the island, Euphemius was quickly sidelined. An initial assault on the island's capital, Syracuse, failed, but the Muslims were able to weather the subsequent Byzantine counter-attack and hold on to a few fortresses. With the aid of reinforcements from Ifriqiya and al-Andalus, in 831 they took Palermo, which became the capital of the new Muslim province. The Byzantine government sent a few expeditions to aid the locals against the Muslims, but preoccupied with the struggle against the Abbasids on their eastern frontier and with the Cretan Saracens in the Aegean Sea, it was unable to mount a sustained effort to drive back the Muslims, who over the next three decades raided Byzantine possessions almost unopposed. The strong fortress of Enna in the centre of the island was the main Byzantine bulwark against Muslim expansion, until its capture in 859.

Habash_al-Hasib_al-Marwazi described the trigonometric ratios: sine, cosine, tangent and cotangent

Around AD 830, Caliph Al-Ma'mun commissioned a group of Muslim astronomers led by Al-Khwarizmi to measure the distance from Tadmur (Palmyra) to Raqqa, in modern Syria. They calculated the Earth's circumference to be within 15% of the modern value, and possibly much closer. How accurate it actually was is not known because of uncertainty in the conversion between the medieval Arabic units and modern units, but in any case, technical limitations of the methods and tools would not permit an accuracy better than about 5%.

A more convenient way to estimate was provided in Al-Biruni's Codex Masudicus (1037). In contrast to his predecessors, who measured the Earth's circumference by sighting the Sun simultaneously from two different locations, al-Biruni developed a new method of using trigonometric calculations, based on the angle between a plain and mountain top, which made it possible for it to be measured by a single person from a single location. From the top of the mountain, he sighted the dip angle which, along with the mountain's height (which he calculated beforehand), he applied to the law of sines formula. This was the earliest known use of dip angle and the earliest practical use of the law of sines. However, the method could not provide more accurate results than previous methods, due to technical limitations, and so al-Biruni accepted the value calculated the previous century by the al-Ma'mun expedition.

Al-Mansur founded a palace library modeled after the Sassanian Imperial Library, and provided economic and political support to the intellectuals working there. He also invited delegations of scholars from India and other places to share their knowledge of mathematics and astronomy with the new Abbasid court.

In the Abbasid Empire, many foreign works were translated into Arabic from Greek, Chinese, Sanskrit, Persian and Syriac. The Translation Movement gained great momentum during the reign of caliph al-Rashid, who, like his predecessor, was personally interested in scholarship and poetry. Originally the texts concerned mainly medicine, mathematics and astronomy but other disciplines, especially philosophy, soon followed. Al-Rashid's library, the direct predecessor to the House of Wisdom, was also known as Bayt al-Hikma or, as the historian Al-Qifti called it, Khizanat Kutub al-Hikma (Arabic for "Storehouse of the Books of Wisdom").

Abu al-Faḍl Jaʽfar ibn Muḥammad al-Muʽtaṣim billāh, better known by his regnal name Al-Mutawakkil ʽalà Allāh (المتوكل على الله, "He who relies on God") was the tenth Abbasid caliph, under whose reign the Abbasid Empire reached its territorial height. He succeeded his brother al-Wathiq. Deeply religious, he is known as the caliph who ended the Mihna (persecution against many Islamic scholars), released Ahmad ibn Hanbal, and discarded the Muʿtazila, but he has been also subject of criticism for being a tough ruler towards the non-Muslim citizens. His assassination on 11 December 861 by the Turkic guard with the support of his son, al-Muntasir, began the troubled period of civil strife known as "Anarchy at Samarra".

The Anarchy at Samarra was a period of extreme internal instability from 861 to 870 in the history of the Abbasid Caliphate, marked by the violent succession of four caliphs, who became puppets in the hands of powerful rival military groups. The term derives from the then capital and seat of the caliphal court, Samarra. The "anarchy" began in 861, with the murder of Caliph al-Mutawakkil by his Turkish guards. His successor, al-Muntasir, ruled for six months before his death, possibly poisoned by the Turkish military chiefs. He was succeeded by al-Musta'in. Divisions within the Turkish military leadership enabled Musta'in to flee to Baghdad in 865 with the support of some Turkish chiefs (Bugha the Younger and Wasif) and the Police chief and governor of Baghdad Muhammad, but the rest of the Turkish army chose a new caliph in the person of al-Mu'tazz and besieged Baghdad, forcing the city's capitulation in 866. Musta'in was exiled and executed. Mu'tazz was able and energetic, and he tried to control the military chiefs and exclude the military from civil administration. His policies were resisted, and in July 869 he too was deposed and killed. His successor, al-Muhtadi, also tried to reaffirm the Caliph's authority, but he too was killed in June 870.

The Battle of Lalakaon was fought in 863 between the Byzantine Empire and an invading Arab army in Paphlagonia (modern northern Turkey). The Byzantine army was led by Petronas, the uncle of Emperor Michael III (r. 842–867), although Arab sources also mention the presence of Emperor Michael. The Arabs were led by the emir of Melitene (Malatya), Umar al-Aqta (r. 830s–863). Umar al-Aqta overcame initial Byzantine resistance to his invasion and reached the Black Sea. The Byzantines then mobilized their forces, encircling the Arab army near the River Lalakaon. The subsequent battle, ending in a Byzantine victory and the emir's death on the field, was followed by a successful Byzantine counteroffensive across the border. The Byzantine victories were decisive the main threats to the Byzantine borderlands were eliminated, and the era of Byzantine ascendancy in the East (culminating in the 10th-century conquests) began. The Byzantine success had another corollary: deliverance from constant Arab pressure on the eastern frontier allowed the Byzantine government to concentrate on affairs in Europe, particularly in neighboring Bulgaria.

Beginning in 902, the dā'ī Abu Abdallah al-Shi'i had openly challenged the Abbasids' representatives in the eastern Maghreb (Ifriqiya), the Aghlabid dynasty. After a succession of victories, the last Aghlabid emir left the country, and the dā'ī's Kutama troops entered the palace city of Raqqada on 25 March 909. Abu Abdallah established the Fatimid Caliphate, a new Shi'a regime, on behalf of his absent, and for the moment unnamed, master.

In 945, Ahmad entered Iraq and made the Abbasid Caliph his vassal, at the same time receiving the laqab Mu'izz ad-Dawla ("Fortifier of the State"), while 'Ali was given the laqab Imād al-Dawla ("Support of the State"), and Hasan was given the laqab Rukn al-Dawla ("Pillar of the State").

One Thousand and One Nights is a collection of Middle Eastern folk tales compiled in Arabic during the Islamic Golden Age. It is often known in English as the Arabian Nights, from the first English-language edition (c. 1706–1721), which rendered the title as The Arabian Nights' Entertainment.The work was collected over many centuries by various authors, translators, and scholars across West, Central and South Asia, and North Africa. Some tales trace their roots back to ancient and medieval Arabic, Egyptian, Indian, Persian, and Mesopotamian folklore and literature.

In particular, many tales were originally folk stories from the Abbasid and Mamluk eras, while others, especially the frame story, are most probably drawn from the Pahlavi Persian work Hezār Afsān, which in turn relied partly on Indian elements.The thing common to all the editions of the Nights is the initial frame story of the ruler Shahryār and his wife Scheherazade and the framing device incorporated throughout the tales themselves. The stories proceed from this original tale some are framed within other tales, while some are self-contained. Some editions contain only a few hundred nights, while others include 1001 or more. The bulk of the text is in prose, although verse is occasionally used for songs and riddles and to express heightened emotion. Most of the poems are single couplets or quatrains, although some are longer. Some of the stories commonly associated with the Arabian Nights—particularly "Aladdin's Wonderful Lamp" and "Ali Baba and the Forty Thieves"—were not part of the collection in its original Arabic versions but were added to the collection by Antoine Galland after he heard them from the Syrian Maronite Christian storyteller Hanna Diab on Diab's visit to Paris.

The Siege of Chandax in 960-961 was the centerpiece of the Byzantine Empire's campaign to recover the island of Crete which since the 820s had been ruled by Muslim Arabs. The campaign followed a series of failed attempts to reclaim the island from the Muslims stretching as far back as 827, only a few years after the initial conquest of the island by the Arabs, and was led by the general and future emperor Nikephoros Phokas. It lasted from autumn 960 until spring 961, when the main Muslim fortress and capital of the island, Chandax (modern Heraklion) was captured. The reconquest of Crete was a major achievement for the Byzantines, as it restored Byzantine control over the Aegean littoral and diminished the threat of Saracen pirates, for which Crete had provided a base of operations.

In 969, the Fatimid general Jawhar the Sicilian, conquered Egypt, where he built near Fusṭāt a new palace city which he also called al-Manṣūriyya. Under Al-Mu'izz li-Din Allah, the Fatimids conquered the Ikhshidid Wilayah, founding a new capital at al-Qāhira (Cairo) in 969. The name al-Qāhirah, meaning "the Vanquisher" or "the Conqueror", referenced the planet Mars, "The Subduer", rising in the sky at the time when the construction of the city started. Cairo was intended as a royal enclosure for the Fatimid caliph and his army—the actual administrative and economic capitals of Egypt were cities such as Fustat until 1169. After Egypt, the Fatimids continued to conquer the surrounding areas until they ruled from Ifriqiya to Syria, as well as Sicily.

Tughril Beg, the leader of the Seljuks, took over Baghdad.

While the Caliph al-Mustarshid was the first caliph to build an army capable of meeting a Seljuk army in battle, he was nonetheless defeated in 1135 and assassinated. The Caliph al-Muqtafi was the first Abbasid Caliph to regain the full military independence of the Caliphate, with the help of his vizier Ibn Hubayra. After nearly 250 years of subjection to foreign dynasties, he successfully defended Baghdad against the Seljuqs in the siege of Baghdad (1157), thus securing Iraq for the Abbasids.

The First Crusade (1096–1099) was the first of a series of religious wars, or Crusades, initiated, supported and at times directed by the Latin Church in the medieval period. The objective was the recovery of the Holy Land from Islamic rule. While Jerusalem had been under Muslim rule for hundreds of years, by the 11th century the Seljuk takeover of the region threatened local Christian populations, pilgrimages from the West, and the Byzantine Empire itself. The earliest initiative for the First Crusade began in 1095 when Byzantine emperor Alexios I Komnenos requested military support from the Council of Piacenza in the empire's conflict with the Seljuk-led Turks. This was followed later in the year by the Council of Clermont, during which Pope Urban II supported the Byzantine request for military assistance and also urged faithful Christians to undertake an armed pilgrimage to Jerusalem.

The Almohad Caliphate was a North African Berber Muslim empire founded in the 12th century. At its height, it controlled much of the Iberian Peninsula (Al Andalus) and North Africa (the Maghreb).The Almohad movement was founded by Ibn Tumart among the Berber Masmuda tribes, but the Almohad caliphate and its ruling dynasty were founded after his death by Abd al-Mu'min al-Gumi. Around 1120, Ibn Tumart first established a Berber state in Tinmel in the Atlas Mountains.

Omar Khayyam was a Persian polymath, mathematician, astronomer, historian, philosopher, and poet. He was born in Nishapur, the initial capital of the Seljuk Empire. As a scholar, he was contemporary with the rule of the Seljuk dynasty around the time of the First Crusade. As a mathematician, he is most notable for his work on the classification and solution of cubic equations, where he provided geometric solutions by the intersection of conics. Khayyam also contributed to the understanding of the parallel axiom.

Al-Nasir Salah al-Din Yusuf ibn Ayyub, better known simply as Salah ad-Din or Saladin (), was a Sunni Muslim Kurd who became the first sultan of both Egypt and Syria, and was the founder of the Ayyubid dynasty. He was originally sent to Fatimid Egypt in 1164 alongside his uncle Shirkuh, a general of the Zengid army, on the orders of their lord Nur ad-Din to help restore Shawar as vizier of the teenage Fatimid caliph al-Adid. A power struggle ensued between Shirkuh and Shawar after the latter was reinstated. Saladin, meanwhile, climbed the ranks of the Fatimid government by virtue of his military successes against Crusader assaults against its territory and his personal closeness to al-Adid. After Shawar was assassinated and Shirkuh died in 1169, al-Adid appointed Saladin vizier, a rare nomination of a Sunni Muslim to such an important position in the Shia caliphate. During his tenure as vizier, Saladin began to undermine the Fatimid establishment and, following al-Adid's death in 1171, he abolished the Fatimid Caliphate and realigned the country's allegiance with the Sunni, Baghdad-based Abbasid caliphate.

The siege of Jerusalem lasted from September 20 to October 2, 1187, when Balian of Ibelin surrendered the city to Saladin. Earlier that summer, Saladin had defeated the kingdom's army and conquered several cities. The city was full of refugees and had few defenders, and it fell to the besieging armies. Balian bargained with Saladin to buy safe passage for many, and the city came into Saladin's hands with limited bloodshed.

In the early years of his caliphate, his goal was to crush the Seljuq power and replace it with his own. He incited rebellion against the Seljuq Sultan of Persia, Toghrul III. The Khwarezm Shah, Ala ad-Din Tekish, at his instigation, attacked the Seljuq forces, and defeated them in 1194. Toghrul was killed and his head exposed in the caliph's palace.

The Siege of Baghdad was a siege that took place in Baghdad in 1258, lasting for 13 days from January 29, 1258 until February 10, 1258. The siege, laid by Ilkhanate Mongol forces and allied troops, involved the investment, capture, and sack of Baghdad, which was the capital of the Abbasid Caliphate at that time. The Mongols were under the command of Hulagu Khan, brother of the khagan Möngke Khan, who had intended to further extend his rule into Mesopotamia but not to directly overthrow the Caliphate. Möngke, however, had instructed Hulagu to attack Baghdad if the Caliph Al-Musta'sim refused Mongol demands for his continued submission to the khagan and the payment of tribute in the form of military support for Mongol forces in Persia.

Hulagu began his campaign in Persia against the strongholds of Nizari Ismailis, who lost their stronghold of Alamut. He then marched on Baghdad, demanding that Al-Musta'sim accede to the terms imposed by Möngke on the Abbasids. Although the Abbasids had failed to prepare for the invasion, the Caliph believed that Baghdad could not fall to invading forces and refused to surrender. Hulagu subsequently besieged the city, which surrendered after 12 days.

During the next week, the Mongols sacked Baghdad, committing numerous atrocities there is debate among historians about the level of destruction of library books and the Abbasids' vast libraries. The Mongols executed Al-Musta'sim and massacred many residents of the city, which was left greatly depopulated. The siege is considered to mark the end of the Islamic Golden Age, during which the caliphs had extended their rule from the Iberian Peninsula to Sindh, and which was also marked by many cultural achievements in diverse fields.

Key Findings:

• The Abbasid historical period is considered the Islamic Golden Age.
• During this period the Muslim world became an intellectual center for science, philosophy, medicine and education.
• Arab scientist Ibn al-Haytham developed an early scientific method in his Book of Optics (1021).
• Medicine in medieval Islam was an area of science that advanced particularly during the Abbasids' reign.
• Astronomy in medieval Islam was advanced by Al-Battani, who improved the precision of the measurement of the precession of the Earth's axis.
• The best known fiction from the Islamic world is The Book of One Thousand and One Nights, a collection of fantastical folk tales, legends and parables compiled primarily during the Abbassid era.
• Arabic poetry reached its greatest height in the Abbasid era.
• Under Harun al-Rashid, Baghdad was renowned for its bookstores, which proliferated after the making of paper was introduced. Chinese papermakers had been among those taken prisoner by the Arabs at the Battle of Talas in 751.
• A major development was the creation or vast enlargement of cities as they were turned into the capital of the empire, beginning with the creation of Baghdad in 762
• Egypt being a center of the textile industry was part of Abbasid cultural advancement.
• Advances were made in irrigation and farming, using new technology such as the windmill.
• Crops such as almonds and citrus fruit were brought to Europe through al-Andalus, and sugar cultivation was gradually adopted by the Europeans.
• Arab merchants dominated trade in the Indian Ocean until the arrival of the Portuguese in the 16th century.
• Engineers in the Abbasid caliphate made a number of innovative industrial uses of hydropower.
• A number of industries were generated during the Arab Agricultural Revolution