Labourers found a skull on Monday of last week when they cut a trench alongside Rue des Mielles, just 100 yards or so from the island's Nunnery building, which contains a Roman fortlet.
The skull, thought to be that of a juvenile or young woman, was recovered along with fragments of leg bone and a cist or tomb cover.
A local archaeologist provisionally dated the skull as late Roman.
On Thursday two more bodies were spotted, as well as a section of wall, so Dr Jason Monaghan, director of Guernsey Museums, flew over to investigate.
He found that the wall, on a clay layer, stood 1.1m below the surface, at an appropriate depth to be Roman.
Investigation of the trench elicited other possible burial cists or walls.
'The natural ground is wind-blown sand, so building stones or dark archaeological features stand out well,' he said.
'One feature turned out to be a cremation capped by a huge boulder. This consisted of charred bones interred in a black urn, which may be of the pre-Roman Iron Age.
'I removed the cremation and its contents as completely as possible. It was brought in several bags back to Guernsey.'
He also hand-excavated the second cist.