Assertion: caliphate's army | /r/HasProperty | umar ibn al-khattāb
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text: In 637, a Muslim army under the Caliph Umar ibn al-Khattāb defeated a larger Persian force led by General Rostam Farrokhzad at the plains of al-Qādisiyyah, and then advanced on Ctesiphon, which fell after a prolonged siege.