Underneath a temple in the ancient ruined city of Taposiris Magna, archaeologists discovered a vast tunnel, referred to by experts as a "geometric miracle".

The structure was discovered 13 metres (43 feet) below the ground by Kathleen Martinez of the University of Santo Domingo in the Dominican Republic and colleagues during an ongoing excavation of the temple. 

The 2-metre tall tunnel had been hewn through an incredible 1,305 metres (4,281 feet) of sandstone.

According to the Egyptian Ministry of Tourism and Antiquities, the tunnel's design is similar to the 1,306-metre Tunnel of Eupalinos - a 6th-century BC aqueduct on the Greek island of Samos, often referred to as a marvel of engineering.

The tunnel's purpose is currently unknown, with parts of it submerged in water.

Martinez, who has been working in Taposiris Magna since 2004 in search of the lost tomb of Cleopatra VII, believes the tunnel to be a promising lead.

Taposiris Magna was founded around 280 BCE by Ptolemy II, the son of Alexander the Great's renowned general and one of Cleopatra's forebears.

The team believes the temple was dedicated to the god Osiris and his queen, the goddess Isis - the deity with whom Cleopatra courted a strong association. 

Figurines of Isis, as well as coins bearing the names and likenesses of Cleopatra and Alexander the Great, have been found there.

Future work could give us more information on whether the new tunnel could lead to these long-lost tombs.

The next steps include exploring the nearby Mediterranean Sea. 

Between 320 and 1303 CE, a series of earthquakes hit the coast, causing part of the temple to collapse and be swallowed by the waves. 

Previous excavations have revealed a network of tunnels stretching from Lake Mariout to the Mediterranean.

The tunnel has already yielded some treasures: a rectangular block of limestone and pieces of pottery.

In 2009, then-Minister for Antiquities Zahi Hawass said, "If we discover the tomb of Cleopatra and Mark Antony, it will be the most important discovery of the 21st century. If we did not discover the tomb of Cleopatra and Mark Antony, we made major discoveries here, inside the temple and outside the temple."