Khalid, the Rashidun general, had already inflicted two defeats on the Sassanid armies before the Battle of Walaja (633 CE), in Mesopotamia. On the battlefield, the Sassanids had numerical advantage, and a sound defensive position, backed against a ridge with their heavy cavalry guarding their flanks. However, Khalid, fast developing a reputation for tactical brilliance, spotted an opportunity. Under cover of night, he sent his light cavalry to the rear of the Sassanids, concealed from view by the ridge. When battle was joined the following day, Khalid ordered his ground troops to make a frontal assault. After withstanding this assault, the Sassanids, as Khalid expected, counterattacked, deploying their heavy cavalry to try and break through the Muslim centre. Khalid ordered his centre to give ground, forming a crescent before the advancing enemy. At the decisive moment, Khalid unleashed his concealed cavalry, completely enveloping the Sassanids, who were then routed with heavy casualties.
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