River Thames Thames Estuary), the river is subject to tidal activity from the North Sea. Before the lock was installed, the river was tidal as far as Staines, about upstream. London, capital of Roman Britain, was established on two hills, now known as Cornhill and Ludgate Hill. These provided a firm base for a trading centre at the lowest possible point on the Thames. A river crossing was built at the site of London Bridge. London Bridge is now used as the basis for published tide tables giving the times of high tide. High tide reaches Putney about 30 minutes later than
Lower Thames Crossing on the A128 at Chadwell St Mary in Essex. In January 2009, the Department for Transport proposed three major options to increase capacity east of London over the River Thames to be built downstream of the existing Dartford Crossing and an additional proposal to increase capacity at the Dartford Crossing. Advocates of the proposal argue that a new crossing is needed to alleviate congestion at the Dartford Crossing. Currently, there is a ferry service operating between Gravesend and Tilbury, which predominantly carries foot passengers and bicycles, Monday to Saturday. A study in a Lower Thames Crossing providing "relief to east