A 10 million square meter underground city has been revealed beneath a famous ancient castle.

Beneath the historic foundations of the ancient Zerzevan castle in Diyarbakir province – southeastern Türkiye – scientists have discovered an incredible settlement.

According to Ancient Origins , the massive excavation, which lasted nine years, revealed a multi-tiered underground city, spanning an area of ​​up to 10 million square meters ^and capable of accommodating thousands of people, hidden beneath the ancient ruins of Zerzevan .

The ruins of the ancient Zerzevan castle - (Photo: AA).

The Daily Sabah reported that the excavations also uncovered fortifications in the form of ramparts and watchtowers surrounding the ancient castle. Meanwhile, the mysterious city beneath the castle contained a church and a canal stretching for at least several miles.

In addition, archaeologists unearthed a seal from the Assyrian era, carved into a stone block dating back three millennia.

One of the "gateways to the underworld" of the ancient castle - (Photo: ANCIENT ORIGINS).

The ancient Zerzevan Castle itself , also known as the Samachi fortress , is a monument with a rich and diverse history. Originally, it was established as a border garrison of the Roman Empire in the 3rd century AD.

This castle was inherited, perfected, and modified over the centuries, primarily during the 3rd to 5th centuries. The castle is now just a ruin, but it still attracts hundreds of thousands of visitors each year, even though the reception center remains unfinished.

During peacetime, approximately 1,500 people, including soldiers and civilians, lived within the castle walls. However, during periods of conflict, the population on the grounds sometimes increased to 10,000, including people seeking refuge.

That could be the reason behind the creation of the mysterious underground city, which has been meticulously renovated.

Approximately six settlements have been unearthed around the castle, within its city walls. Archaeologists estimate that there are up to 100 such settlements hidden beneath the surface.

According to NPR, the excavation is still ongoing in the hope of shedding light on this unusual way of living. What has been unearthed includes administrative buildings and astonishing weapons caches .

"The excavation area we are working on inside the castle walls is 57,000 ^{square meters} . That's a huge area, and outside it could be up to 10 million square meters ^, " said Turkish archaeologist Aytac Coskun, who is leading the excavation.