Black Gate is the mid 13th century stone gatehouse of a barbican, founded by King Henry III. Flanking the exposed western curtain wall and defending the North Gate of Newcastle Castle it was the last medieval addition. Of four storeys and attic, the lower part is roughly oval and the upper is octagonal, to the fore is a square projection. Very little remains of the medieval layout, except the vaulted chambers on either side of the central passage which are thought to have been guardrooms. It's original height remains unknown because the second and third stories were remodelled with original stone in the early 17th century. The fourth floor and roof were then rebuilt in the late 19th century when the gatehouse was converted into a museum and library by the Society of Antiquaries of Newcastle Upon Tyne.