Kurds vs Mongols

Fadlullah Hamadani, the historian of the Ilkhanate from the 14th century, claims that the Mongols' discovery of the Kurds' kryptonite led to the conquest of the Hawler/Erbil citadel:

Hamadani (14th-century): 

When Hülägü Khan set out to conquer Baghdad, he assigned the Arbela fortress to Uruqtu Noyan. It is a bastion set firmly upon a glacis and has no like in the inhab-ited quarter of the globe. When Urugtu Noyan laid siege, the Kurds began to fight from the citadel, and Tajuddin Ibn Salaya, the lord of Arbela, came to surrender and performed good services. Uruqtu said, "The sign of your true surrender will be the turning over of the citadel." Tajuddin went to the citadel gate, but the Kurdish soldiers would not let him in. After much insistence he gave up and came away, returning to Uruqtu, who sent him to Hülägü Khan. He was found guilty at a trial and executed.

Uruqtu besieged the citadel for a time, but the defenders refused to give in. Then he requested reinforcements from Sultan Badruddin Lu'lu'. He sent a few soldiers. One night the defenders of the citadel came down and launched a surprise attack on the Mongols, killing all they could find, setting their catapults ablaze, and retreating into the citadel. Uruqtu was stunned and sum-moned Badruddin Lu'lu' for consultation. Badruddin Lu'lu' said, "The best plan is to postpone this until summer, when the Kurds will flee from the heat and go into the mountains, for now the weather is nice and they have plenty of supplies. The citadel is highly impregnable and impossible to take except by stealth." Uruqtu stationed Sultan Badruddin there and went to his summer pastures in Tabriz. When the weather turned hot, the Kurds came down, turned the citadel over to Sultan Badrud-din, and went to Syria. Sultan Badruddin destroyed the ramparts, and thus the citadel was also conquered.