Fortifications of London

Beheaded traitors often had their head stuck on a spike on London Bridge, then their body quartered and spread among the gates.

After the curfew, rung by the bells of St Mary le Bow and other churches at nine o'clock, or dusk, (whichever came earlier) the gates were shut.

The gates were also used as checkpoints, to check people entering the City, and to collect any tolls that were being charged for the upkeep of the wall, or any other purpose that might require money.

The drawbridge served a double function; firstly it could form an impassable barrier to any force attacking from the south and secondly, whilst allowing merchant vessels to pass upstream to the dock at Queenhithe, when lowered it could prevent enemy ships from passing to attack from the rear.

[1] During World War I, part of the London Defence Positions scheme was resurrected to form a stop line in the event of a German invasion.

In the city the Cabinet War Rooms and the Admiralty Citadel were built to protect command and control centres, and a series of deep-level shelters prepared, as refuge for the general population against bombing.

[3] Work on these lines was halted weeks later by Ironside's successor, General Alan Brooke,[4] who favoured mobile warfare above static defence.

The Corporation of the City of London responded by altering the layout of access roads to the city and putting in checkpoints to be manned when the threat level warrants it; these measures are known as the "ring of steel" a name taken from the more formidable defences that, at that time, ringed the centre of Belfast.

The rest of London (with the exception of obvious targets such as Whitehall, the Palace of Westminster, the Royal residences, the airports and some embassies) do not have such overt protection, but London is heavily monitored by CCTV, and many other landmark buildings now have concrete barriers to defend against truck bombs.