The ancient city of Hasankeyf is perched on rock, towering above the river Tigris.

It is a spectacular setting filled with monuments to multiple civilisations.

The caves at the very top are 3,000 years old.

More recent sandstone mosques in the valley below testify to a time when Hasankeyf was among the richest cities in Mesopotamia.

Soon the entire valley is to be flooded with a dam. The controversial project was first conceived in 1954 and abandoned six years ago.

Now a new funding deal from an international consortium including Austria, Germany and Switzerland means it is on the brink of realisation.

Environmental activists are horrified.

"The castle of Hasankeyf is a million years monument made by nature, the Tigris and the rocks. Can you imagine all this will sink for only 50 years economic benefit?" asks Nuri Ozbagdatli.

"You can transport the dam plans to wherever suitable. But you cannot carry nature and the archaeological heritage from here."

Economic development

The 1.2bn euro (£816m) Ilisu dam is part of Turkey's vast GAP project - a network of dams and hydroelectric power plants along both the Tigris and Euphrates rivers.

It will flood more than 300 sq km (116 sq miles) of land to create the second largest reservoir in the country.

The aim is to generate electricity to feed rapidly rising demand and fuel Turkey's economic development.

Dam supporters also argue it will help develop the neglected south east of Turkey, racked by years of conflict with Kurdish separatists.

Many locals migrated away from the violence and the poverty. Now some are starting to come back because of the dam.

At least 4,000 jobs should be created.

In the small, dusty town closest to the dam site - but out of the flood zone - a new restaurant has just opened, in anticipation of hungry construction workers and their families.

Other locals are building additional floors on their houses to rent out.

"I wish Hasankeyf wasn't flooded. But most people here can't find jobs," says teacher Benjamin Alp, playing backgammon in the shade on a side street.

"There's no industry, nothing. So people do want the dam to find work."

"This region has a lot of economical problems," his friend Ridvan agrees.

"The economic benefits of the dam will help people improve their situation and prevent them choosing other ways," he says - referring to support for the outlawed Kurdish separatist PKK.

Rich history

But the cost to history will be high.

The dam consortium plans to create a culture park on the edge of the reservoir and transfer key monuments from Hasankeyf there.

That includes the remains of a 900-year-old bridge, built when Hasankeyf was the capital of the Artukid Empire - and now the symbol of the city.

Most experts argue the sandstone much of Hasankeyf is built from will crumble if it is moved.

They scorn the notion the city can be recreated in a culture park.

Archaeologists also believe there are layers rich with history beneath ground they will not have time to reach before the flood.

So they are working against the clock to recover whatever possible.

This month the dig team uncovered fragments of the first Roman wall mosaic ever found here.

"For an archaeologist who has been working here for years nothing can be so painful as seeing all these artefacts flooded," says excavation leader Abdusselam Ulucam, as he brushes the dust of centuries from his new discovery.

"We are constantly bringing things to light here from the smallest stone to big walls. Knowing that all this will vanish far from human eyes is deeply upsetting."

New opportunities

Fifty-four thousand people will be displaced by the dam in total.

Those who live in Hasankeyf will be offered new apartments nearby. Others will get compensation.

But it is another major upheaval in the mainly Kurdish-populated region, where tens of thousands have already been forcibly displaced during the worst years of fighting here.

The man in charge of the dam says his project will leave those people better off and he is convinced he is doing no harm to history.

"Nine sites will be transported to a culture park. The new appearance will be marvellous!" Yunus Bayraktar enthuses.

The project co-ordinator has a vision of caves converted to villas, crowds of tourists - and jet skis.

He points out that the uppermost part of Hasankeyf will remain above water and suggests any monuments that cannot be moved can be rebuilt - leaving the originals as an underwater paradise for divers.

"The cultural heritage in Hasankeyf is collapsing in any case. It only has eight or so years left to survive," he argues.

"This project will transfer it to the next centuries."

The dam consortium says this is the only viable location for their reservoir.

They want to generate tourist revenue here as well as electricity.

Opponents insist they are drowning at least 3,000 years of history in the process.