Complex sentence: This was a stronghold of the kingdom of Dalriada until the 9th century (possibly its center at one time) and believed to have held the Stone of Destiny before its transfer to Scone Palace.
Split into simpler sentences: This was a stronghold of the kingdom of Dalriada until the 9th century, and possibly its centre at one time. It is believed to have held the Stone of Destiny before its transfer to Scone Palace.