Archaeologists have discovered a long-lost slice of history submerged deep beneath the surface of the Adriatic Sea. The UNESCO World Heritage site of Aquileia is hailed as one of the best preserved Roman cities in Italy, having once been one of the biggest and most bustling towns in the ancient empire.

But parts of the city have lain hidden beneath the waves after being swallowed by the surrounding sea centuries ago. And now, underwater experts have made some striking finds while exploring these areas, most notably two shipwrecks and a mysterious, unidentified monument.