Archaeologists made a staggering discovery underneath the world's oldest city, uncovering 4,000 canals that would have fed over 700 farms. Eridu in southern Mesopotamia, or modern-day Iraq, presents one of the most well-preserved ancient archaeological sites.

It's believed to be around 5,400 years old and was abandoned in 600 BC. Durham University researchers said the extensive network of canals dates back to before the first millennium BC and was used by farmers to irrigate their fields. The study, led by Jaafar Jotheri, was published in the journal Antiquity and mapped the canals, which remained undisturbed for centuries as the river Euphrates shifted its course. Eridu was therefore left dry and uninhabited, preserving it like no other Mesopotamian region with irrigation systems that ended up buried under new canals.

Satellite and drone images, as well as fieldwork, identified 200 primary canals and 4,000 smaller branches. The primary canals, between 0.6 and 5.5 miles long and 2-5 metres wide, joined the river Euphrates.

They would have been used by farmers to irrigate water from high river levees to the surrounding fields, with breaks in the levees distributing the flow across the floodplain.

This system then evolved over centuries as different parts of it were used at different times.

However, the researchers noted that more studies are required to gain further insight into the agricultural practices and management of the floodplain in the modern era.

The researchers wrote: "Both sides of the river were canalised and farmed, although farmers exploited the northern side more heavily than the southern side.

"Canals require immense labour and experience in water management to operate successfully.

"Therefore, it is essential to conduct additional research on the chronology of the canals to better understand changes in the irrigation systems and agricultural landscape over time."