Like most people, I wish whoever defaced this statue had found some other means of venting his rage. Imagine what a splendor it would be if the entire figure, face and all, were still largely intact and looking much like it did when it was first erected.

I don't know whether the defacing (literally) was religiously motivated, as some muslims sometimes frown on depicting the human figure, especially the face.

Well, here there was no human figure to deface, so I assume the iconolasts settled for doing a real number on this creature's human face.

Alternatively, the damage might have been inflicted by Alexander the Great's men when the sacked and burned the palaces at Persepolis ca. 330 BCE.

According to the Lonely Planet guide to Iran,

"Whenever important foreign delegations arrived [at Persepolis], their presence was heralded by trumpeters at the top of the [Grand Stairway] . . ."

"Acolytes then led the dignitaries through Xerxes' Gateway (also known as the Gate of All Nations), which is still a wonderfully impressive monument."

"The gateway was built during the time of Xerxes I [486 - 465 BCE] and is guarded by bull-like figures that have a strong Assyrian character. . . ."

Above [the figures a] . . . cuneiform inscription in Old Persian, Neo-Babylonian and Elamite . . . declares, among other things, that