Complex sentence: During its pre-history the area which later became Ripon was under the control of Brythonic tribe the Brigantes, and three miles (5 km) north at Hutton Moor there is a large circular earthwork created by them.
Split into simpler sentences: During its pre-history the area which later became Ripon was under the control of the Brigantes, a Brythonic tribe. Three miles (5 km) north at Hutton Moor there is a large circular earthwork created by them.