The Tower (C4)

THE Titanic was unsinkable. The Tower of London was impregnable. That's what they thought, although it turned out to be wrong in both cases.

The builders of the London landmark had reckoned without a bunch of revolting peasants protesting about the poll tax. Led by Wat Tyler, the mob broke into one of the most secure buildings in Britain and rampaged through the royal apartments in 1381.

Collusion with gatekeepers was suspected, although that was small comfort for Archbishop Simon Sudbury, who was dragged from the Tower and brutally beheaded. His 600-year-old naturally mummified head is kept in a church in Sudbury as a gruesome legacy of the incident.

That was one of the few times in almost 1,000 years that the defences have been breached. Hardly surprising as you need to get through six gates, three drawbridges and two portcullises to penetrate the place.

For most of us, the Tower is somewhere you visit to see the Crown Jewels and those yeoman warders in their fancy uniforms. But there's a lot more to the Tower than that as this eight-part series aims to prove. Each episode concentrates on a particular aspect of the castle's history, with the opener concentrating on its function as a fortress.

There was much excitement at the lowering of a portcullis, dating back 700 years. No one alive has ever seen this down, we were told. Tension mounted, and cameras clicked, as the spiked door slowly emerged.

The experts were puzzled by what looked like a cat flap, although they decided eventually that it was probably a cannon port not a pussy portal.

Much screen time was given over to footage of the Ceremony of the Keys, the world's longest unbroken military tradition. This involves a yeoman warder, soldiers, cries of "Halt, who comes here?" and much jangling of keys. The security ritual begins at precisely 9.53pm and 53 seconds, to ensure that the final turn of the key comes as the clock strikes ten.

It seems an awful lot of fuss just to lock the doors at night. Even then, someone once forgot to put the cat out, as the mummified body of a black feline found in the foundations of the White Tower goes to show. If only that had been a cat flap in the portcullis, the poor moggy might have survived.