It was once a flourishing Bronze Age city that thrived on trade and art, but the ancient site of Haft Tappeh in modern Iran has also been hiding a dark secre

Archaeologists excavating the ruins of the 4,000-year-old city, which was a major centre of the Elamite empire, have discovered a mass grave containing hundreds of skeletons.

They believe the dead, which includes children that were haphazardly piled on top of each other behind a wall, were the victims of a brutal massacre that occurred around 3,400 years ago.

Archaeologists working on the ancient ruins of Haft Tappeh in modern day Iran have discovered a mass grave (pictured) containing hundreds of skeletons piled up against a wall. The bodies may belong to victims of a massacre that occurred towards 3,400 years ago, when the city appears to have been in decline

The killings seem to coincide with a time when building work in the city had halted and the community began to decline.

Historians have been puzzled as to why the urban development of Haft Tappeh seems to have stagnated suddenly after several hundred years of prosperity and growth.

WHAT WAS HAFT TAPPEH? Haft Tappeh is thought to be the site of an ancient city that dates back to 1500BC. Sometimes known as Kabnak, it is thought to have been an important political centre during the reign of the Elamite king Tepti-Ahar. The Elamites was a pre-Iranic civilisation that centred in the far west of modern-day Iran. It first began to appear around 2700BC before disappearing in 539BC. While the Elamite capital was largely based in the city of Susa, it is thought that Tepti-Ahar moved his capital to Haft Tappeh. A large tomb was built in the city to house the king and his family after he died. Skeleton remains found in the tomb are thought to belong to the Royal family but their identities have yet to be confirmed. Advertisement

The discovery suggests the city's population may have fallen victim to a brutal conflict, perhaps as rival groups battled for control.

The king of the Elamite empire at the time, Tepti-ahar, is thought to have been the last in the ruling Kidinuid dynasty and the skeletons may have been victims of the unrest that followed his death as competing families fought for control.

Behzad Mofidi-Nasrabadi, an archaeologist from Johannes Gutenberg University Mainz in Germany who has been leading the excavation, said: 'Based on the number of skulls, we excavated 149 individuals.

'In the unexcavated part of the trench there should be another 100 to 150 skeletons.

'Some of the skulls and bones seem to belong to children.

'Between the skeletons we found some pottery vessels from the Middle Elamite period. Also some date kernels were found.

'Although there is no indication for an ordinary burial, it seems that some people tried to give the deceased scarce nutriment as grave goods.

'The large number of deceased led to the assumption that there took place either a massacre or an epidemic.'

Haft Teppeh (shown) is thought to have been a political centre of the Elamite empire 4,000 years ago in what is now southwest Iran. Archaeologists discovered the site in 1908 but were unable to access it until the 1970s

Excavations at the site in southwest Iran have previously revealed large building complexes (pictured) and temples in the city, which at its height covered an area of 617 acres. But the richly decorated buildings appear to have been abandoned and the building materials were used to construct smaller homes

A statement posted by the Johannes Gutenberg University Mainz added: 'The dead had simply been haphazardly piled one on top of another behind a wall.'

The Elmaite empire was a pre-Iranic civilisation that centred in the far west of modern-day Iran. It first began to appear around 2700BC before disappearing in 539BC.

The Kidinuid dynasty were the fourth family of kings thought to have ruled over the empire and rose to power in the 15th Century.

The capital of the empire was the city of Susa, but under the rule of Temti-Ahar it appeared to move to the city of Haft Tappeh.

Archaeologists first discovered the ruins of the city in the Khuzestan Province of southwest Iran in 1908.

Intricate pieces of jewellery, copper cups and pottery (pictured) have been discovered at the site of Haft Tappeah, suggesting it had a rich culture of crafts, art and trade

Statues made from terracota were also found at the site, suggesting it was once a prosperous city with a rich cultural heritage. However, the mass grave suggests all did not end well for the population

After further excavations in the 1970s the site then became inaccessible until 2007 when German archaeologists were able to return to the area.

The excavations have previously revealed a large temple on the site where the god Kirwashir was worshipped and a large underground Royal tomb was unearthed beneath it.

The temple appears to have been decorated with bronze plates and wall paintings while intricate carvings and jewellery have also been discovered at the site.

Other large structures - including an administrative centre containing clay tablets written on in cuneiform script in the Akkadian language - are among the other discoveries.

However, archaeologists have also found evidence that many of the large buildings appear to have been abandoned between 1400BC and 1500BC, with the materials being used to construct simple houses.

Previous excavations in 2007 uncovered a large administrative building where clay tablets were discovered, detailing some elements of what life was like in the city

A statement posted on the website of Johannes Gutenberg University Mainz said: 'Within a relatively short period of time, the Elamite kings Tepti-ahar and Inshushinak-shar-ilani built here monumental structures such as temples and palaces, and the area covered by the city was extended to roughly 250 hectares (617 acres).

'The city continued to flourish for about one hundred years, and trade and political relations with neighboring states such as Babylon were established.

'A discovered workshop with attached clay tablet archive provides ample evidence of the expansion of commerce, arts, and crafts.

'At the end of the 14th century BC, the urban developments in Haft Tappeh stagnated for reasons that are as yet unknown.'