The River Parrett, the Bristol Channel and the Severn Estuary are believed to have been used for riverine bulk transportation of people and supplies in Somerset under Roman and later Anglo-Saxon and Norman occupation. Roman Somerset, which lasted for over 250 years until around the beginning of the 5th century, had various settlements, including Bath (Aquae Sulis), Ilchester (Lindinis) and lead mines at Charterhouse; and four roads surrounding the Somerset Levels. There is evidence of two Roman ports on the Parrett. The port at Combwich, on the west bank, was ill-recorded before its destruction by quarrying and erosion. The other at Crandon Bridge on the east bank near where the current King's Sedgemoor Drain enters the Parrett, was in use between the first and the fourth centuries. Evidence of an extensive site with storehouses was found in the mid-1970s, during motorway construction works. The Crandon Bridge site may have been linked by a probable Roman road over the Polden Hills to the Fosse Way, at Ilchester. Ilchester, the largest Roman town in Somerset, was a port with large granaries, sited where the Fosse Way crossed the Ilchester Yeo by means of a paved ford. The Yeo was navigable by small craft all the way to the Parrett allowing military supplies to be brought by boat directly to Ilchester; however, disembarkation at Crandon Bridge and use of the Polden Hills roadway allowed more rapid movement to Ilchester. The Yeo may already have been straightened and canalised before Roman occupation.