Complex sentence: Evidence of huge fires on the banks of the Avon between the two avenues also suggests that both circles were linked, and they were perhaps used as a procession route on the longest and shortest days of the year.
Split into simpler sentences: Evidence of huge fires on the banks of the Avon between the two avenues also suggests that both circles were linked. They were perhaps used as a procession route on the longest and shortest days of the year.