Mohenjo Daro likely was, at its time, the greatest city in the world. Roughly 4,500 years ago, as many as 35,000 people lived and worked in the massive city, which occupies 250 acres along Pakistan’s Indus river.

Mohenjo Daro sat beneath the soil for thousands of years, a preserved relic of the ancient Indus Valley civilization. But excavation exposed the city to the elements, and now, says the Telegraph, the ruins may have as little as 20 years left.

he once lost city is in danger of disappearing again as its clay wall houses, grid system roads, great granaries, baths and drainage systems crumble to dust, a victim of government neglect, public indifference and tourists’ fears of terrorism. Archaeologists have told The Sunday Telegraph that the world’s oldest planned urban landscape is being corroded by salt and could disappear within 20 years without an urgent rescue plan.

Last year, heavy flooding threatened the ruins, but even outside of natural disasters the town is fading fast.

Preservation work has been going on since the first major excavations in 1924 and intensified after it was made a World Heritage Site in 1980, but the effort has flagged as scarce government funds have been diverted by earthquakes and floods, officials said. They need 350 labourers, as well as masons, supervisors and technical staff, but on the day The Sunday Telegraph visited there were just 16 men wheeling barrows of mud to shore up the walls.

More from Smithsonian.com:

Flooding in Pakistan Threatens Remains of 4500-Year-Old Civilization

Can Computers Decipher a 5,000-Year-Old Language?