Archaeologists have unearthed a forgotten city hidden in Saudi Arabia's desert oasis that was constructed by an advanced society 4,000 years ago.

The fortified city, called al-Natah, was home to at least 500 people who were once nomads, but constructed at least 50 multi-story buildings in 2400 BC.

The ancient civilization built giant tombs that housed their remains and metal weaponry, like axes and daggers, which experts said showed they were 'advanced.'

Al-Natah was subdivided into a residential area, a decision-making zone and a necropolis that was connected by small streets and long-trade networks.

Pottery fragments were also found among the dwellings, hinting at an egalitarian society that prioritized the city's survival.

This type of society is a community where there is no social hierarchy and every person is considered equal regardless of gender, race, class or wealth.

The 269,000-square-foot settlement was hidden in a walled desert oasis of Khaybar in the Arabian peninsula. 

When the city was built, other areas ranging from along the Mediterranean Sea from modern-day Syria to Jordan were flourishing, but the oasis was previously thought to be a barren wasteland dotted with tombs and nomads.

The earliest known city in human history was called Çatalhöyük, a settlement of about 10,000 people that existed in modern-day Turkey from 7400 BC to 5200 BC. 

But researchers found that unlike previous cities, the ancient al-Natah people had built a process of 'slow urbanism' where small, organized communities gradually adapted to life in the desert. 

Pastoral nomads roamed northwest Arabia since the beginning of the first millennium BC and among them was the Bedouin tribe which hunted, traded and raided villages to obtain goods.

They relied on their herds of goats, sheep and camels for food, cheese, milk and other needs and would form family groups called clans that protected members from other nomadic tribes.

Archaeologists at the French National Center for Scientific Research in Paris reported that local nomads had decided to settle down into a new community in the early Bronze Age to protect themselves from raids.

The team said that al-Natah had been overlooked for so long because of the black volcanic rock - basalt bedrock that covered the area.

The basalt had concealed it to such a degree that it 'protected the site from illegal excavations,' French archaeologist and the study's lead author, Guillaume Charloux told AFP. 

Al-Natah was first discovered 15 years ago when researchers observed the site using satellites from above that revealed paths and the foundation of houses.

They created a 3D rendering of what the city looked like 4,000 years ago and said that although they identified only 50 dwellings, many may have been dismantled over the millennia.

That suggested the real number could be between 55 and 70 houses.

According to the study, the structures' thickness and configuration indicated that most were two or three stories tall and all had foundations that were likely used for storage or crawl space.

'This type of construction is reminiscent of traditional Arabian tower houses, particularly the much later ones in the Najd region,' the study, published in the PLOS journal, said.

A subdividing wall separated the dwellings from a necropolis filled with 'stepped tower tombs' - a high, circular tomb that had an exterior wall and inner burial chamber lined with stone pillars.

These tombs suggested that residents conducted intricate burial practices, while weaponry found in the burial sites indicated that the people had a distinct knowledge of metal working.

The discovery of weapons combined with a fortified wall extending 8.9 miles around the city indicated that the people created a way to defend themselves against potential raids, further cementing their early urban lifestyle. 

The largely populated area and wall indicated that the residents laid the foundation for an 'incense route' that involved trading spices, frankincense and myrrh from southern Arabia to the Mediterranean. 

Several wells and water sources were identified at the site, including one located as the base of a nearby cliff that would have provided residents with a good water supply. 

These findings are 'proof that these ramparts are organized around a habitat,' Charloux told AFP. 

The city was abandoned between 1500 BC and 1300 BC for reasons unknown, but researchers speculated that they could have left the area to return to nomadic life, because of disease or climate deterioration.