Whom does Alexander the Great attack in this scene from the "Alexander Mosaic" found at the House of Faun in Pompeii?

Porus, Hindu Emperor
Bessus, the Satrap of Bactria
Darius III of Persia
Memnon of Rhodes
The Alexander Mosaic, dating from circa 100 BC, is a Roman floor mosaic originally from the House of the Faun in Pompeii. It depicts a battle between the armies of Alexander the Great and Darius III of Persia. The original is preserved in the Naples National Archaeological Museum. The mosaic is believed to be a copy of an early 3rd-century BC Hellenistic painting.
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