One of a number of London Stones
Link this one stands beside the Thames at the mouth of Yantlet Creek. It marked the downstream limit of the control of the river by the City of London Corporation. The corresponding marker on the other side of the river is
TQ8585 : The Crowstone near Southend-on-Sea, which can be seen in the background of this picture. The line between these stones is the "Yantlet Line" which is still used as a boundary for various things
Link .
The corresponding marker above London is
TQ0271 : London Stone, Staines at 31 km as the crow flies upstream from London Bridge. But this stone at Yantlet is 54 km downstream.
Direct access to the stone is difficult because
TQ8777 : Grain Marsh is an MoD firing range. To take this photo, I approached from
TQ8478 : The British Pilot in Allhallows and paddled through Yantlet Creek.