“Since the magic moment when I first opened my eyes in the sea, I have never been able to see, think or live as I did before,” wrote the French pioneer of underwater exploration, Jacques Cousteau.

A fascination with the unseen world beneath the surface of the oceans covering two-thirds of our planet has long gripped the human imagination: but marine exploration gains a new poignancy when the worlds discovered underwater are human.

This summer, two exhibitions of marine archaeology open windows on to past civilisations. “Sunken Cities: Egypt’s lost worlds” at the British Museum (until 27 November) throws a fascinating light on the long lost ancient Egyptian cities of Thonis-Heracleion and Canopus recently rediscovered at the mouth of the Nile.

Meanwhile, “Storms, War and Shipwrecks: Treasures from the Sicilian Seas” at Oxford’s Ashmolean Museum (until 25 September) brings together an intriguing collection of underwater finds illuminating 2,500 years of the island’s history from the Phoenicians to the Normans.

While early discoveries off the coast of Sicily were made by local fishermen, over the past two decades technological developments in marine archaeology have facilitated the excavation of ancient sites buried, like the Nile cities, under metres of sediment.