Alexander sent the bulk of his army to the Persian ceremonial capital of Persepolis via the Persian Royal Road. Alexander himself took selected troops on the direct route to the city. He then stormed the pass of the Persian Gates (in the modern Zagros Mountains) which had been blocked by a Persian army under Ariobarzanes and then hurried to Persepolis before its garrison could loot the treasury. On entering Persepolis, Alexander allowed his troops to loot the city for several days. Alexander stayed in Persepolis for five months. During his stay a fire broke out in the eastern palace of Xerxes I and spread to the rest of the city. Possible causes include a drunken accident or deliberate revenge for the burning of the Acropolis of Athens during the Second Persian War by Xerxes. Even as he watched the city burn, Alexander immediately began to regret his decision. Plutarch claims that he ordered his men to put out the fires, but that the flames had already spread to most of the city. Curtius claims that Alexander did not regret his decision until the next morning.