As St Ives was founded on the banks of the wide River Great Ouse between Huntingdon and Ely, it had become an important entrepôt for trade in East Anglia. The size and prosperity of the medieval town can be still seen in its street plan. In the early 15th century, St Ives Bridge was constructed across the Great Ouse replacing an earlier crossing at this point. The six-arch stone bridge was one of only four town bridges in England to have a chapel. In the Early Medieval period, this had been a strategic location on the Great Ouse because it was the last natural crossing point or ford on the river, from the sea. A flint reef in the riverbed created a ford; it was reused as the foundations for the stone bridge. Throughout the medieval period, it was a source of income for the town as tolls had to be paid by all those wanting to cross, this especially applied to drovers bringing their livestock to market.