One of the most famous bas-relief at Persepolis has a lion biting a bull. Mostly animals and humans are shown in profile. But the full frontal face of the lion is depicted here. Perhaps a sign of how important it is.
One interpretation, that I read about, says that the scene depicts Nowruz, the Persian New Year. Nowruz marks the first day of Spring or Equinox, and the beginning of the year in the Persian calendar. The lion is the sun, and the bull is the moon. They are equal in power on this day. Nowruz is important for Zoroastrians, the faith of the Achaemenid Empire of Cyrus and Darius, who built Persepolis.
Another interpretation, that I heard from our Iranian tour guide, says that the lion is the king and the bull represents bounty. The king sheds the blood of the bull, which nourishes the land, his domain. It sounds more romantic and even heroic.