In 1118 Roger captured Azaz, which left Aleppo open to attack from the Crusaders; in response, Ilghazi invaded the Principality in 1119. Roger marched out from Artah with Bernard of Valence, the Latin Patriarch of Antioch. Bernard suggested they remain there, as Artah was a well-defended fortress only a short distance away from Antioch, and Ilghazi would not be able to pass if they were stationed there. The Patriarch also advised Roger to call for help from Baldwin, now king of Jerusalem, and Pons, but Roger felt he could not wait for them to arrive.

Roger camped in the pass of Sarmada, while Ilghazi besieged the fort of al-Atharib. Ilghazi was also waiting for reinforcements from Toghtekin, the Burid emir of Damascus, but he too was tired of waiting. Using little-used paths, his army quickly surrounded Roger's camp during the night of June 27. The prince had recklessly chosen a campsite in a wooded valley with steep sides and few avenues of escape. Roger's army of 700 knights, 500 Armenian cavalry and 3,000 foot soldiers, including turcopoles, hastily formed into five divisions. During the battle, Roger was killed by a sword in the face at the foot of the great jewelled cross which had served as his standard. The rest of the army was killed or captured; only two knights survived. Renaud Mansoer took refuge in the fort of Sarmada to wait for King Baldwin, but was later taken captive by Ilghazi. Among the other prisoners was likely Walter the Chancellor, who later wrote an account of the battle. The massacre led to the name of the battle, ager sanguinis, Latin for "the field of blood."

Ilghazi was defeated by Baldwin II of Jerusalem and Count Pons at the Battle of Hab on August 14, and Baldwin took over the regency of Antioch. Subsequently, Baldwin recovered some of the lost towns. Even so, the defeat at the Field of Blood left Antioch severely weakened, and subject to repeated attacks by the Muslims in the following decade. Eventually, the Principality came under the influence of a resurgent Byzantine Empire.