It was not until 1434 that Alnwick was licensed to build a defensive wall. The building of the town wall took at least 50 years, and it is not certain that it was ever completed. The wall is thought to have been about two metres thick and six metres high.
Streets subsequently developed along the line of the wall. Starting from Bondgate Tower, it ran along Hotspur Street, Green Bat (ex Back Row), Tower Lane, Dispensary Street and Northumberland Street. Before reaching Bailiffgate, it turned towards the Castle. From the Castle it follows close to Greenwell Road back to the Bondgate Tower.
It is thought that there were four towers which provided entrances to the town. (A report of 1770 states the town had three towers one of which had no roof.)
- Bondgate Tower is the only remaining remnant of the medieval defences.
- Pottergate Tower stands on the site of the medieval tower, but was totally rebuilt in 1768 and was given a crown at that time. Following storm damage the crown was removed in 1812.
- Clayport Tower was demolished in 1804.
- Narrowgate Tower is still a mystery. It is not known definitively if it existed, and if it did, where it was located.