The lower portion of the river, from the sea to Ford, was navigable in the eleventh century at the time of the Norman conquest. In the sixteenth century, Henry FitzAlan, 19th Earl of Arundel built wharves at Ford, and improved the river channel below there, so that the town became a port. Over the 30 years from 1544, he also improved the river as far upstream as Pallingham Quay. Although the work involved a number of flash locks, which were not very successful, no tolls were charged for its use, and vessels of around 15 tons were used to carry timber. Attempts to make the river navigable up to Newbridge in the early sixteenth century were not successful.