‘Garden vat’. Pink granite. L. 205 cm. Ptolemaic Period, IVth-IInd century BC. Thonis-Heracleion, Aboukir Bay (SCA 459). Image Credit: ©Franck Goddio / Hilti Foundatio

For more than a thousand years, the statues of a king and his queen lay broken and abandoned in the murky waters of the Nile delta.

Youthful posthumous portrait of Alexander the Great, 2nd-1st c. BC; from Alexandria

They had once stood outside a temple, proud red granite figures five metres tall decorated with the symbols of power — he with the double crown embellished with a serpent, she with a crown of cow horns, sun and feathers, the dress of a royal wife.

They were lifted from the sea bed by French diver-cum-archaeologist Franck Goddio and have been restored to take their place alongside hundreds of artefacts in “Sunken Cities, Egypt’s Lost Worlds” at London’s British Museum.

Like the royal couple, the lost cities of Canopus and Thonis-Heracleion have lain beneath the sea long forgotten, the subject only of occasional academic conjecture. But they were flourishing ports in the seventh century BC, built on neighbouring islands in a marshy region criss-crossed by canals — not unlike medieval Venice. The foundations were unstable, the sea levels rose in the Mediterranean and the weight of the temples was too great to withstand the tsunami or earthquake that hit them in the late eighth century AD.

Goddio has taken 20 years to reclaim the artefacts that comprise this mesmerising exhibition but it was in 1933 that a British Royal Air Force pilot taking off from an air base on the Bay of Abukir, on the Mediterranean coast of Egypt, glimpsed the outline of ruins under the sea.

He contacted a prominent Egyptian scholar Prince Omar Toussoun, who with the help of fishermen discovered of ruins of what was Canopus, with red granite statues and marble columns stretching for about 150 metres, about two kilometres from the shore

The show’s co-curator Aurélia Masson-Berghoff says the findings have completely transformed the understanding of the relationship between Greece and Egyptian civilisations during the last half of the first millennium BC when Greek traders first settled around the mouth of the Nile.

Furthermore, Goddio’s discoveries have solved a problem that has puzzled Egyptologists over the years: that Heracleion, famed in legend as the hiding place 3,000 years ago for Paris and his lover Helen of Troy when they were on the run from her angry husband Menelaos, was one and the same as Thonis, as the Egyptians called it.

A statue Hapy made of red granite, from the temple of Thonis-Heracleion

A statue of Osiris, from the Egyptian Museum in Cairo

The importance of the cities as trading centres can be gauged by a stele found by Goddio from 380BC, which records a royal decree on the taxation of trade to Thonis-Heracleion. It is in immaculate condition, spelling out in 14 columns of hieroglyphic text, how his majesty Nectanebo I ruled that “one-tenth of the gold, of the silver, of the timber, of the processed wood and all things coming from the sea ... are reckoned for the benefit of the royal domain”.

As these tax rights were the same as imposed by Heracleion, the two had to be the same.

These were busy ports — as the 69 foreign ships and 700 anchors found by Goddio testify. And there are entertaining details that bring them to life, such as a Greek amphora from 550-500BC, which contained wine imported from Greek cities in Turkey to the Egyptian elite. One Greek trader, Charaxos, who was the brother of Sappho of Lesbos, travelled to Egypt with a consignment of wine only to fall for the charms of a local courtesan and spent a fortune to release her from slavery.

Many of the statues and artefacts are in good condition, thanks in part to the sand that helped preserve them and hide them from possible thieves.

The role of the king and queen had been to protect the temple of Amun-Gereb in Thonis-Heracleion from about 285-246BC and they might have been part of a triumvirate that included a fertility figure known as Hapy. Another monumental statue, Hapy is not just the first of Goddio’s findings, but it is the first thing the visitor sees, or not. The museum plays a little game. In fact, the first sight is a disappointingly blank screen. Step behind it, and there — in a terrific coup de theatre — towers Hapy, a colossal red granite statue almost 18 feet tall.

He seems to be striding towards the visitor, just as he did centuries ago, taking offerings of wine, food and water to the pharaoh. It is an awe-inspiring spectacle made the more compelling because he stands alone in an empty room against a murky blue backdrop. It is as if he is coming out of the sea.

The life-size statue of a queen, possibly Cleopatra III from the second century BC, is also taking a step forward in the Egyptian way. She wears a royal diadem with the sacred rearing cobra and holds a musical instrument, as one might expect from an Egyptian ruler, but much of the style of the sculpture is Greek with her hair in a cork screw and a garment wrapped around her to emphasise her shape. Her almond-shaped eyes were once inlaid with gold but are now empty.

Even more indicative of the interaction between the two civilisations — and more ravishing — is Arsinoe II who was venerated by both Greeks and Egyptian in the third century BC. She had married her brother Ptolemy II and was worshipped with her statue outside every temple.

Although it was decapitated in AD391 when Christians ransacked a temple in Canopus, the statue in black granodiorite — an igneous rock — is nonetheless remarkable with bare shoulders and diaphanous robes. The sculpture represents her as the Greek deity Aphrodite but there is something of the catwalk model about her in her unabashed confidence.

Not everything that is beautiful has to be big. There are hundreds of objects that bring this lost civilisation to life in fascinating detail — a gilded silver goblet from the first or second century richly decorated with scenes of Dionysos, the deity of wine with his satyrs and cupids, a silver coin with the head of Alexander the Great wearing an elephant scalp as a headdress, a tiny pottery perfume bottle, decorated with the image of a panther.

There are a number of gold rings and earrings, terracotta moulds of amulets in the form of scarab beetles or Egyptian deities and symbols, incense burners, bronze bowls and even examples of divine false beards in bronze, which would have been fixed to a statue of a Pharaoh.

Few objects are more striking than the 10.5-inch tall bronze statue of Osiris, the Egyptian deity of afterlife, whose eyes inlaid with gold glare across the centuries, or more poignant than a tiny lead container still with the offering of food to the deity preserved inside.

As videos with images of divers working in swirling sand and misty waters remind us the exhibition is almost as much about the work that Goddio and his team have carried out over the past 20 years as about the discoveries they have made. One UK newspaper described him as a cross between marine explorer Jacques Cousteau and Indiana Jones.

The difficulty of finding ruins scattered over 110 square kilometres in the deep sediment of the delta and lifting such colossal statues, which, like Hapy, weighed six tonnes, required intensive planning.

First they studied whatever texts and documents mentioned Canopus and Thonis-Heracleion, such as writings by the Greek historian Herodotus who visited the Nile in the fifth century BC, as well as Egyptian papyri and stone inscriptions. They spent months mapping out the area and getting everything prepared before they could send a diver into the water.

They used sophisticated technology to discover where the artefacts lay hidden, such as echo sounders that produced a bathymetric or underwater relief map, magnetic devices to provide clues about the location and size of the artefacts and sidescan sonar that measured the shadows of the artefacts and gave an idea of their size. Once located, down went the scuba divers using a water dredge, an underwater suction device, to clear the sediment and allow the explorer to find the artefacts, however small.

The two cities have already yielded a spectacular haul, but less than 5 per cent has been investigated so far and for Goddio’s team the exploration goes on. “There is another 100 years of work to be done here,” he says.

Richard Holledge is a writer based in London.

“Sunken Cities, Egypt’s Lost Worlds” runs at the British Museum in London until November 27.