Cripplegate was originally the northern entrance to the Roman fort, built c.AD120. This Roman gate probably remained in use until at least the late Saxon period when it is mentioned in 10th and 11th century documents. The gate was rebuilt in the 1490's. Throughout its history Cripplegate had a variety of uses. It was leased as accommodation and also, like the more famous Newgate, used as a prison.
After the restoration of Charles II in 1660 all of the City gates were unhinged and the portcullises wedged open making ceremonial entrances before being demolished.
Cripplegate gave access to a substantial medieval suburb and of the village of Islington. Extra defensive works outside the gate gave rise to the name Barbican which was subsequently taken as the name for the post-WW2 rebuilding of the area.
The information above comes from an information board about the London Wall, at the Cripplegate site.
Cripplegate would have been across Wood Street at the site of the plaque with London Wall extending from it, to the east and to the west.