Discovery made during cleaning of lake floor.

A marble head has been found in Lago di Nemi, leading to speculation that it could once have decorated Emperor Caligula's ships best associated with the small volcanic lake near Rome.

The mysterious discovery was made during routine works to clean the bed of the lake in the Castelli Romani town at the weekend, according to Italian news sites.

For now there is no official confirmation on the exact nature of the find and the local administration has invited the public "to respect the integrity and delicacy of the site where the discovery was made", reports La Repubblica newspaper.

The mayor of Nemi "hopes that this discovery will shed new light on the history of Caligula and his legacy, allowing the secrets hidden in the depths of Lake Nemi to be revealed again," reports news agency Dire.

The archaeological remains of the two lavish ceremonial ships, built under the reign of Caligula in the first century AD, were recovered between 1928 and 1932 after Mussolini ordered the draining of the lake.

The enormous ships, which had been hidden 18 metres below the lake surface for centuries, were subsequently housed in a nearby purpose-built museum which was destroyed by fire on the night of 31 May 1944, during world war two.

The purpose of the ships, one larger than the other, remains the source of speculation, with the larger vessel believed to have been an elaborate floating palace, which contained marble floors and mosaics, fountains, heating, plumbing and baths.