Entrances to important buildings were frequently ‘protected’ by pairs of colossal animals (some of which were mythological guardian creatures) in the ancient Near East.
The bodies of the bulls were carved in relief on the side walls of the portico, whereas the heads were carved in the round.

Sometime in the past, perhaps when Persepoli was sacked, the heads became detached from their bodies. They were found not far from the bodies during excavations in 1932/3 by archaeologists . Unfortunately, the ears and horns, which were clearly not carved from the same block of stone but added separately, were not recovered