Man knocked down wall in his house to find underground city that once had 20,000 people living there

A man once found an enormous underground city in his basement while searching for the reason his chickens kept disappearing.

During the remodel he noticed that a small crevasse had formed in his basement and his chickens were disappearing through it, never to return.

His discovery was the first of more than 600 entrances which were eventually found inside people's homes which lead to the Derinkuyu underground city.

Excavation work uncovered an incredible marvel of engineering, a network of tunnels and shelters 18 levels deep that went down 280ft (85 metres) which could keep up to 20,000 people and their livestock safe from harm for a time.

This enormous underground city is thought to have begun life as a system of caves built back 1200 BC by the Hittites to shelter from the Phrygians, who then in turn further excavated the area and expanded the living space when they conquered the region.

In later centuries it appears as though Christian inhabitants of the Roman Empire expanded the cave systems by adding more layers and including chapels, stables and places to make wine and olive oil.

The underground city of Derinkuyu was a safe haven for the people living in the region on many occasions, with a long string of conquerors and occupiers marching through that part of the world.

For centuries it was used by the Christian citizens of the Byzantine Empire to shelter from Muslim raiders, and it was during this time that the underground city was most busy.

Following the Byzantine collapse, the local Christian population used it to hide from Ottoman persecution for several centuries more.

Derinkuyu, located in Anatolia, is in a part of the world that has been conquered and invaded plenty of times, making a hidden city where 20,000 people could hide a very handy thing to have.

While the city itself may have been ancient it had only been hidden for around 40 years as it had been abandoned when many of Anatolia's Christians were forcibly evicted from their homes and sent to Greece in a population exchange in 1923.

The underground city was built to protect its inhabitants from harm, complete with rolling boulders able to be moved to block corridors, and would not have been a place where people lived all the time.

Chimneys running down through the structure ensured the inhabitants seeking refuge had air to breathe, and space to bring livestock down meant people could stay fed as they sheltered from whatever was threatening them this time.

Animals were kept closer to the surface to avoid the smell from their dung making the city uninhabitable, while storerooms indicated that people seeking shelter could stay underground for months at a time if possible.

These days the underground city is a tourist attraction you can delve into, provided you're not too claustrophobic.