Yantlet

London Stone is the name given to a number of boundary stones which stand beside the rivers Thames and Medway, which formerly marked the limits of jurisdiction of the City of London.

Until 1350, the English Crown held the right to fish the rivers of England and charged duties on those people it licensed to fish. In 1197 King Richard I, in need of money to finance his involvement in the Third Crusade, sold the rights over the lower reaches of the River Thames to the City of London. Marker stones were erected to indicate the limit of the City's rights.

In Victorian times, the Lord Mayor would come in procession by water and touch the Staines stone with a sword to re-affirm the City's rights.

Control of the river passed from the City to the Thames Conservancy, and then below Teddington to the Port of London Authority and above it to Thames Water Authority and finally the Environment Agency.

In medieval times before the canalisation of the Thames, Staines-upon-Thames was the highest point at which the high tide was perceivable for a few minutes every semi-diurnal tide (twice a day), adding some millimetres to the water depth compared to more upstream parishes. This London Stone marked the upstream limit of the City's rights. The official role of a London Corporation stone of 1285 beside Staines Bridge was set out with a grant of associated privileges in a charter of Edward I. Its use by the river is confirmed by the semi-circular indentations (on the right hand face in the photo), to cater to tow ropes of horse-drawn boats rubbing against the stone.

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Wikipedia