How difficult would it be sailing across the North Sea in a massive wooden boat with only a primitive sun-compass for navigation? The Vikings managed it, so in Secrets of the Ancients, an international crew decided to give it a go in a replica Viking long boat. Kind of makes our everyday reliance on the A to Z rather pathetic.

Julius Caesar claimed that during the Gallic wars, he had built a sturdy wooden bridge across the Rhine, over which he marched an entire army, in just ten days. A couple of thousand years later, this series looks on as engineer Chris Wise uses Caesar's own recorded account in an attempt to recreate this engineering feat over the North Tyne.

The mathematician Archimedes invented a terrifying machine known as The Claw, which was used successfully against the Romans when they attempted to conquer Syracuse. Despite the slight inconvenience that there is no record of the machine's appearance or its mechanism, engineer Jo da Silva attempts to recreate it for Secrets.

The Olmec civilization in Mexico sculpted massive stone heads 3000 years ago ? 500 years before Rome was founded. These statues weighed up to 40 tonnes and were made from stone that came from the Tuxtla mountains more than 160 kilometres away. The journey would have taken the Olmecs across great rivers and virtually impassable swamps. How did they manage that?

A lot of people have heard of The Hanging Gardens of Babylon, but few know why these gardens were considered by the Greeks to be one of the Seven Wonders of the World. The irrigation system alone is a mystery worthy of its own Secrets episode. How were such elaborate gardens watered? No one really knows, but attempts to test various theories have been made by modern water engineers using technology of the time and this series follows those attempts. At least these Babylonians didn't have to face the modern-day difficulty of a hose-pipe ban.