The intriguing find was made some 20 feet below Liverpool Street as workers bored through ancient river sediments from the long-vanished Walbrook River, once a tributary of the Thames. The skulls and pottery shards found with them may have collected in a bend of the old river, having washed down from a nearby burial ground.

The Roman skulls and pottery are just the latest in a staggering number of archaeology marvels that have been uncovered by the $23 billion (£14.8 billion) subterranean Crossrail engineering project. The project aims to create a new underground rail line beneath London. (See "London's Underground Revealed.")

The finds cut across history—everything from 9,000-year-old Mesolithic stone tools, to medieval plague pits, to a 16th-century graveyard associated