The Lorteburn or Langbourne is a lost stream or river, which ran in the east of the City of London, arising near to Aldgate, flowing south near to the Tower of London, and discharging into the River Thames. The stream appears to have been covered over or dry by the early 14th century but its course has been discovered during archaeological digs in the area and the water shed can be traced in the street level contours of that part of the city as mapped by Kelsey in 1841. The stream gave its name to the Langbourn ward of the city. The river is seldom included on maps or lists of London's lost rivers, and its existence is denied by Nicholas Barton, in his 1962 book Lost Rivers of London, but in more recent work David Bentley argues for its existence. Toponymy The name Lorteburn is attested in a deed of 1288, when the stream was still extant. The name Langbourne is attested in Stow in 1603, when it had been dry for nearly two centuries. In English River Names, Eilert Ekwall identifies several instances of Lorteburn. He gives the derivation as from an Old English word meaning dirt or filth. Related to the Old Norse lortr ("excrement, faeces"), this implies a dirty or filthy stream, possibly one used for a sewer. There is a second possibility given by Ekwall, a derivation from either the brook name Hlōra, or the mythical Norse female name Hlóra. The brook name derived from the Old English hlōwan meaning "The roaring one". This implies a swift stream with foaming water. This derivation may seem unlikely given the short length of the stream, but the watercourse was steep, and 'roaring' does correspond with Stow's description. Burn or Bourne is a standard name for smaller streams and river, common in the area of London, for example the nearby rivers Ravensbourne, Tyburn and Westbourne. In place names it normally means 'stream'. Archaeological evidence In 1981, David Bentley assembled evidence for the stream's existence, relying on archaeological and map evidence, especially in the records of the Museum of London. He first points out there is a shallow linear valley in that part of the city, first identified by Richard Kelsey's topographical survey in 1841. The topography of this part of London has been changed almost beyond recognition since the 1841 survey, especially by the construction of the London,