Armed with laser rangefinders, GPS technology and remote control robots, a group of speleologists is completing the first ever mapping of the aqueducts of ancient Rome on archaeology's "final frontier".

They abseil down access wells and clamber through crevices to access the 11 aqueducts that supplied Rome, which still run for hundreds of kilometres (miles) underground and along stunning viaducts.

The mission of these "speleo-archaeologists" is to update the last above-ground map of the network compiled at the beginning of the 20th century by British Roman archaeologist Thomas Ashby....