Israeli authorities have recovered a Roman-era sarcophagus that construction workers sought to hide after digging it up at a building site, officials said Thursday.

The limestone coffin, estimated at 1,800 years old and discovered last week during work on a new neighbourhood in coastal city Ashkelon, was described as "unique" by Gabi Mazor, a retired Israel Antiquities Authority archaeologist and expert on the era.

The contractors who encountered the find opted to extract it themselves with a tractor, damaging it before hiding it beneath a stack of metal sheets and boards, according to the authority.

Police have questioned the contractors on suspicion of not reporting their find and of damaging it, and the authority pledged that legal proceedings would be pursued against those involved.

An authority spokeswoman said they did not know why the contractors had attempted to conceal the find.

Mazor said the decorations on the sarcophagus were particularly noteworthy.

"All its sides are decorated, with very impressive and beautiful decorations. Quite a few sarcophagi are found in Israel, but nearly none of them are decorated, and those that are usually have wreaths and other floral themes" and not much more, he said.

The lid of the sarcophagus has an image of a man -- apparently representing the deceased -- leaning on his left arm, wearing a short embroidered shirt, with Roman-style curls and no beard, implying he was young.

Around the coffin are engraved images of "bulls' heads, naked Cupids, and the head of the monstrous female figure Medusa which includes remains of hair together with snakes, part of a commonly held belief in the Roman period that she protects the deceased," Mazor said.

Ashkelon was at the time a mixed city, comprised of pagan Romans and Jews, as well as Samaritans, but Mazor said the decorations leave little doubt the sarcophagus belonged to a Roman.

The presence of the two-tonne, 2.5-metre (eight-foot) long sarcophagus at the construction site suggested there may be a mausoleum and other coffins at the site.