From over 600,000 years ago , during the Pleistocene ice age , until the Anglian Stage around 478,000 to 424,000 years ago , the early River Thames flowed through the area where Chelmsford now stands , from Harlow to Colchester , before crossing what is now the North Sea to become a tributary of the Rhine .
From over 600,000 years ago , the early River Thames went through the place where Chelmsford is now , from Harlow to Colchester .