The North Gate was one of the Castle’s more important defensive structures.
The gate was constructed at the vulnerable neck of the Durham Peninsula, and was the entrance to the outer bailey, forming part of the northern line of defence.
Its defensive importance meant that it was often added to over the centuries, each addition making it a more formidable defensive structure. In fact, the gate's re-fortification in the early 15th century was the last significant defensive addition to the Castle.
In later years the gate was used as the county jail. This continued until 1820 when the Bishop of Durham (Barrington) provided the necessary funds to build a new prison, allowing the demolition of the gate which, by then, was seen as dysfunctional and an obstruction to traffic.