 In 577 Ceawlin advanced from the Thames Valley across the Cotswolds to seize the area and break the power of the Britons in the lower Severn area.Some historians (such as Welbore St Clair Baddeley in 1929) have concluded that the Saxons may have launched a surprise attack and seized the hill fort at Hinton Hill Camp (Dyrham Camp) because it commanded the Avon Valley, and disrupted communications north and south between Bath and her neighbouring Romano-British towns of Gloucester and Cirencester.Once the Saxons were in occupation of the site (and had begun reinforcing the existing Iron Age defensive structures at the site) the Britons of those three towns were compelled to unite and make a combined attempt to dislodge them.