1. A marine archaeologist from IEASM examines a column from the Greek-style (tholos) temple.

The temples that fell under the waves

Underwater archaeologists from the European Institute for UnderwaterArchaeology (IEASM) led by Franck Goddio continue to make dramatic discoveries in the Bay of Aboukir in Egypt. Excavation work carried
out by the 2019 mission in the sunken city of Thonis-Heracleion has located part of the remains of a temple devoted to the god Amun-Gereb, which slid into a canal during the catastrophe that overwhelmed the city centuries ago. Dense clay from the Nile has preserved the remains of the temple, which lies at a depth of up to 12ft (3.5m). Finds include architectural fragments, ritual objects, coins, jewellery and statuettes.

2. A Byzantine coin found on the site of Canopus, Aboukir Bay, Egypt.

Although only a small part of the building has been excavated, it appears that its debris filled the canal across a distance of around 300ft (circa 90m), indicating that it was of a particularly impressive size. To the west of the Egyptian temple the archaeologists have also found the remains of a small round Greek-style temple (similar to the Tholos of Delphi), which was destroyed in the same disaster. In ancient times, the city of Thonis-Heracleion was situated at the mouth of the Canopic branch of the River Nile.

3. A Byzantine gold earring found on the site of Canopus, Aboukir Bay, Egypt.

Any boat arriving from, or leaving for the Greek world had to call at the city which acted as a defensive gateway to the Egyptian kingdom. But it was a religious centre too; all new pharaohs had to attend the main temple to be invested with their titles of power as sovereign serving under their chief god Amun.

Archaeologists have established that the main Egyptian temple and the Greek temple date back to the 30th dynasty, or the first part of the 4th century BC. Landslides, they believe, initiated by an earthquake, caused
a tidal wave that engulfed the city in the middle of the 2nd century BC, during the reign of Ptolemy VIII. These caused the city to sink some 20ft (circa 6m) beneath the waters of the Mediterranean Sea leaving only several small islets.

4. Bronze coin, perhaps minted in the area, early 4th century BC.

Today, using new geophysical surveying equipment, the mission working on the site of the nearby city of Canopus has uncovered a new section half a square mile in area. The buildings in the new area are south of the temples and a Christian monastery, previously found, and include various Roman structures, including a bathhouse and other buildings which have yet to be identified. Occupied from the time of the 6th century BC to the 8th century AD, Canopus was destroyed and submerged by a natural disaster, like the city of Thonis-Heracleion.

Franck Goddio and his team have been working in the Bay of Aboukir, which lies 30km east of Alexandria since the late 1990s. The remains of the city of Canopus were discovered in 1999 and the site of Thonis-Heracleion was located in 2001. The team's ongoing work prompts the development of new techniques in marine archaeology yielding up a remarkable range of treasures.

• Franck Goddio and the IEASM work in collaboration with Egypt's Ministry of Antiquities, with the support of the Hilti Foundation. (www.ieasm.institute/institute.php)

Diana Bentley