This stone relief shows the struggle between a bull and a lion. This is a very ancient Iranian motif, known from the fourth millennium BC.

Also, a symbol of Zoroastrian Nowruz - in day of a spring equinox power of eternally fighting bull (personifying the Moon and Earth), and a lion (personifying the Sun and Spring), are equal.
This image represents the return of the sun to the earth, at the time of Nowruz.