Brighton lies between the South Downs and the English Channel to the north and south, respectively. The Sussex coast forms a wide, shallow bay between the headlands of Selsey Bill and Beachy Head; Brighton developed near the centre of this bay around a seasonal river, the Wellesbourne (or Whalesbone), which flowed from the South Downs above Patcham. This emptied into the English Channel at the beach near the East Cliff, forming “the natural drainage point for Brighton”.

Behind the estuary was a stagnant pond called the Pool or Poole, so named since the medieval era. This was built over with houses and shops from 1793, when the Wellesbourne was culverted to prevent flooding, and only the name of the road (Pool Valley, originally Pool Lane) marks its site. One original house survives from the time of the pool’s enclosure. Behind Pool Valley is Old Steine (historically The Steyne), originally a flat and marshy area where fishermen dried their nets. The Wellesbourne occasionally reappears during times of prolonged heavy rain; author Mark Antony Lower referred to an early 19th-century drawing of the Royal Pavilion showing “quite a pool of water across the Steyne”.