Our modern idea of tyranny was born 2,000 years ago. It is with the reign of the Caligula - the third Roman emperor, assassinated in 41 AD, before he had reached the age of 30 - that all the components of mad autocracy come together for the first time.

In fact, the ancient Greek word "tyrannos" (from which our term comes) was originally a fairly neutral word for a sole ruler, good or bad.

Of course, there had been some very nasty monarchs and despots before Caligula. But, so far as we know, none of his predecessors had ever ticked all the boxes of a fully fledged tyrant, in the modern sense.

There was his (Imelda Marcos-style) passion for shoes, his megalomania, sadism and sexual perversion (including incest, it was said, with all three of his sisters), to a decidedly odd relationship with his pets. One of his bright ideas was supposed to have been to make his favourite horse a consul - the chief magistrate of Rome....