Question: what is the difference between london bridge and tower bridge

title: London Bridge
text: With the end of Roman rule in Britain in the early 5th century , Londinium was gradually abandoned and the bridge fell into disrepair . In the Saxon period , the river became a boundary between the emergent , mutually hostile kingdoms of Mercia and Wessex . By the late 9th century , Danish invasions prompted at least a partial reoccupation of the site by the Saxons . The bridge may have been rebuilt by Alfred the Great soon after the Battle of Edington as part of Alfred 's redevelopment of the area in his system of burhs , or it may have been rebuilt around 990 under the Saxon king Æthelred the Unready to hasten his troop movements against Sweyn Forkbeard , father of Cnut the Great . A skaldic tradition describes the bridge 's destruction in 1014 by Æthelred 's ally Olaf , to divide the Danish forces who held both the walled City of London and Southwark . The earliest contemporary written reference to a Saxon bridge is c. 1016 when chroniclers mention how Cnut 's ships bypassed the crossing , during his war to regain the throne from Edmund Ironside ( see Battle of Brentford ( 1016 ) ) .