This vitual checkpoint is part of the City of London's "Ring of Steel", a security cordon set up around London's financial district in the 1990s after a series of bombings by the IRA. It consists of a variety of interventions into the streetscape at major thoroughfares into the designated protected area. These include street narrowing chicanes, bollards, gates, sentry boxes, and surveillance cameras. It was initially erected to protect the financial area but has since slowly grown in size. A system of cameras monitor traffic into the area, capturing drivers faces and vehicle licence plate numbers. If either of these are in the central computer's database a police person standing in the sentry box is alerted and can step out in time to stop the vehicle.