This settlement dominated the pottery trade in what is now central southern England, and pottery was distributed by boats on the Thames and its tributaries. Competition for the use of the river created the centuries-old conflict between those who wanted to dam the river to build millraces and fish traps and those who wanted to travel and carry goods on it. Economic prosperity and the foundation of wealthy monasteries by the Anglo-Saxons attracted unwelcome visitors and by around AD 870 the Vikings were sweeping up the Thames on the tide and creating havoc as in their destruction of Chertsey Abbey. Once King William had won total control of the strategically important Thames Valley, he went on to invade the rest of England. He had many castles built, including those at Wallingford, Rochester, Windsor and most importantly the Tower of London. Many details of Thames activity are recorded in the Domesday Book. The following centuries saw the conflict between king and barons coming to a head in AD 1215 when King John was forced to sign the Magna Carta on an island in the Thames at Runnymede. Among a host of other things, this granted the barons the right of Navigation under Clause 23. Another major consequence of John's reign was the completion of the multi-piered London Bridge, which acted as a barricade and barrage on the river, affecting the tidal flow upstream and increasing the likelihood of the river freezing over. In Tudor and Stuart times, various kings and queens built magnificent riverside palaces at Hampton Court, Kew, Richmond on Thames, Whitehall and Greenwich. As early as the 1300s, the Thames was used to dispose of waste matter produced in the city of London, thus turning the river into an open sewer. In 1357, Edward III described the state of the river in a proclamation: "... dung and other filth had accumulated in divers places upon the banks of the river with ... fumes and other abominable stenches arising therefrom." The growth of the population of London greatly increased the amount of waste that entered the river, including human excrement, animal waste from slaughter houses, and waste from manufacturing processes. According to historian Peter Ackroyd, "a public lavatory on London Bridge showered its contents directly onto the river below, and latrines were built over all the tributaries that issued into the Thames." During a series of cold winters the Thames froze over above London Bridge: in the first Frost Fair in 1607, a tent city was set up on the river, along with a number of amusements, including ice bowling.