Did the river Mersey once flow in the opposite direction to its flow today? The theory is that the Mersey was once a modest river running into the river Dee near Chester across the flat land between Stanlow and Chester and that either an earthquake or a shifting of sands at the present mouth of the Mersey caused the river to change its direction around 1400 years ago. “The evolution of a coastline: Barrow to Aberystwyth ” by William Ashton (1920) propounds this theory. The Roman mapmaker Ptolemy did not show the Mersey at all in his charts. This could be simply an error, as Ptolemy was said to have worked on the basis of information provided by sailors rather by direct observation. Or it could be an accurate statement of fact. Sir J. Allanson “It was in the sixth century that a great tidal wave overwhelmed parts of Winchester and Rye in Sussex and the land of Lyonesse, west of Cornwall was sunk.” The writer’s theory was that the land had sunk from 30 to 45 feet in the last fourteen centuries. “The Mersey’s outlet to the sea was not, down to a date which may have been anywhere between the fourth and ninth centuries, as it is now, along the pre-glacial depression between Liverpool and Birkenhead but it was a tributary of the Dee, which it joined just below Chester.” Picton said that if this was not an error “the estuary of the Mersey in its present form did not exist” at that time. The Chambré Hardman Archives and the Proudman Laboratory website also make references to this theory.