Islamabad — Its millennia-old clay walls have borne silent witness to countless floods in the Indus River valley over the centuries, but officials say this year's catastrophic monsoon season could overwhelm Pakistan's ancient archaeological site of Mohenjo-daro. Most of the ruins, which sit in the country's inundated southern province of Sindh, date back around 4,500 years. It's a UNESCO World Heritage Site, and considered to be among the best-preserved ancient urban settlements in all of South Asia.

Now a calamity that scientists say the modern, developed world bears much of the blame for is devastating millions of lives across Pakistan, and damaging the archaeological treasure in the process.

Mohenjo-daro was first discovered in 1922, but mystery still surrounds the disappearance of the civilization that once thrived there, which coincided with those of ancient Egypt and Mesopotamia. The enigmatic script used by the city-state's people has never been deciphered, so little is understood about their beliefs or customs.

The death toll from the monsoon flooding that has left an estimated third of Pakistan underwater stood Wednesday at 1,325, including 466 children. The disaster has impacted some 33 million people across the country. Now officials say Mohenjo-daro is another victim, with the punishing rains already causing significant damage to the site.