The town’s oldest features are the town walls, ancient earth ramparts surrounding the town, likely built by Alfred the Great in the 9th century to defend the town from the Danes as part of his system of burh towns. The Danes invaded and occupied Wareham in 876, and only left after Alfred returned with an army and made a payment of Danegeld. In 998 they attacked again, and in 1015 an invasion led by King Canute left the town in ruins. The town was a Saxon royal burial place, notably that of King Beorhtric (d. 802). Also in the town at the ancient minster church of Lady St. Mary is the coffin said to be that of Edward the Martyr, dating from 978. His remains had been hastily buried there and were later taken from Wareham to Shaftesbury Abbey in north Dorset (and now lie in Brookwood Cemetery, Surrey). By the end of the Saxon period, Wareham had become one of the most important towns in the county, to the extent that it housed two mints for the issue of Royal money. The Burghal Hidage lists the town as 1,600 hides, the third largest in the realm. After the conquest of England, the Normans built a castle on the banks of the River Frome, at the site now known as Castle Close. The castle was the focus of much fighting between the forces of Stephen and Matilda during the period of civil war in the mid 12th century. The keep was destroyed at an unknown date in the 12th or 13th century, possibly under the terms of the Treaty of Wallingford, and no visible trace remains. Up until this time Wareham had been an important port; however the growth of Poole and the gradual silting of the river caused a decline in trade and by the end of the 13th century most of the foreign trade had transferred to Poole. Local trade continued to be handled at the Quay until the construction of the railway in the 19th century. During the English Civil War, Wareham changed hands several times between the Royalists and Parliamentarians and in August 1644 was the site of a fierce battle with 2,000 Cromwellian soldiers besieging the town.