Complex sentence: In the excavations at Persepolis, archaeologists have found a standard, depicting a falcon ("shahin") with open wings, regarding which the current belief is that this was the official flag of Iran under Cyrus the Great and his heirs.
Split into simpler sentences: In the excavations at Persepolis archaeologists found a standard depicting a falcon ("shahin") with open wings. The current belief is that this was the official symbol of Iran under Cyrus the Great and his heirs.