Join Dan Snow as he explores one of the world's most fortified islands, discovering Roman ramparts, Victorian gun emplacements and giant underground bunkers built by the German occupiers during the Second World War.

Alderney may be a tiny scrap of land in the English Channel - part of the Channel Islands archipelago - but its size belies its importance. It's played an important strategic part in British and French history. Despite only being ten miles west of La Hague on the Cotentin Peninsular, the island has for roughly a thousand years mostly belonged to the English and British. And for this reason, the island has a wealth of historical sites, quite out of proportion to its small size, from Roman walls to impressive concrete bunkers built by the Wehrmacht during the Second World War.

Measuring just three square miles, the island of Alderney remains one of the most heavily fortified places in the world after it was transformed into an impregnable fortress as Hitler looked to strengthen his Atlantic wall. But the island's wartime story didn't end there. The majority of the island's population were evacuated to the mainland prior to the occupation, but a small number chose to return to their homes despite the trials of living alongside the enemy. The two communities weren't alone, they were joined by thousands of foreign labourers - slave labour - who endured meagre rations and rampant disease. To house the influx of POWs, the German occupiers built four camps on Alderney, including Lager Sylt - the only concentration camp on British soil.

In this video, Dan Snow visits a host of Alderney's historic sites starting with the Roman Wall overlooking St Peter's Port to the Odeon - a terrifying concrete tower on the northern tip of the island.