It will come as no surprise to London's frustrated commuters, but linguistic analysis suggests that the city's name may have originated in a warning to travellers of a difficult route ahead.
Research by Richard Coates, professor of linguistics and dean of the school of cognitive and computing sciences at the University of Sussex, has tracked the roots of the name to a pre-Celtic culture far older than previously suspected.
He has identified two concepts at its heart - an ancient word for a river and another implying difficulty in crossing. "The essence of the name was already in place at least 2,500 years ago, meaning something like 'river that can't be simply forded'," Professor Coates said.
The Romans called the city "Londinium", which developed into London. But the name is meaningless in Latin, suggesting it was based on a pre-existing word.
London's previous occupants were the British Celts. But Professor Coates said that their language made little sense of the name.
This led him back to the people who lived in the region before the Celts arrived at least 2,500 years ago. Linguists have been able to get a sense of the Indo-European tongue that preceded British Celtic from place names found across Europe. Professor Coates said that this revealed London's possible meaning as well as the root of the name "Thames", meaning "dark".
Jon Cotton, lead curator of the Museum of London's London Before London gallery, said Professor Coates's analysis echoed research undermining the idea that London was a "greenfield" site when the Romans arrived.
Professor Coates's research is published in his co-authored book Celtic Voices: English Places .