Geography of Kent and Dungeness have been formed by accumulation of alluvium. Kent's principal river, the River Medway, rises near Edenbridge and flows some 25 miles (40 km) eastwards to a point near Maidstone, when it turns north. Here it breaks through the North Downs at Rochester before joining the River Thames as its final tributary near Sheerness. The river is tidal as far as Allington lock, but in earlier times cargo-carrying vessels reached as far upstream as Tonbridge. The Medway has captured the head waters of other rivers such as the River Darent. There are other rivers in Kent, most notably the
Maidstone in Kent to be turnpiked was from Rochester to Maidstone, in 1728. The A20 runs through the town and the M20 motorway runs to the north. Opened in 1960 as the "Maidstone Bypass" A20(M), this was the first motorway south of London. Maidstone is a hub for major roads: the M20 motorway, the A229, A249, A20 and A26. The M2 motorway is a short distance to the north and the A21 also runs close to the town. The historic centre of the town is largely pedestrianised or with restricted access for private vehicles, which are diverted around a one way