First discovery on Tiber riverbed by new underwater heritage protection unit.

Three massive Roman columns have been discovered at the bottom of the river Tiber by underwater archaeologists together with carabinieri divers.

The marble columns were found in almost "zero visibility" waters where the Tiber meets the Fossa Traiana, the artificial canal established by Emperor Trajan to connect Portus, ancient Rome's harbour, with the river Tevere.

The discovery is the result of the first operation carried out by the Underwater Heritage Protection Service, newly established by the Archaeological Park of Ostia Antica, with the help of divers from belonging to the carabinieri and Rome's cultural heritage protection unit.

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The successful first outing by the new underwater team, headed by underwater archaeologist Alessandra Ghelli, found the columns at a depth of five metres.

Partially buried in the river bed and embankment, the columns exceed one metre in diameter and two and a half metres in length, and have yet to be reclaimed from the murky waters.

Alessandro D'Alessio, director of the Ostia Antica archaeological park, told news agency ANSA that during their next operation the divers will attempt to take samples to determine the type of marble and its origin.

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Their efforts are hampered by almost non-existent visibility in the waters which are reportedly clogged with rubbish, animal carcasses, debris and mud.

The three columns have been photographed and registered in the database of the Comando Carabinieri per la Tutela del Patrimonio Culturale (TPC) who will seek to establish that they are not stolen.

So how did they get there in the first place?

The most likely reason for the columns' presence in the water is the result of a boat sinking in ancient Roman times, according to D'Alessio, who recalls that the Tiber was widely used for the transport of goods and materials.

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D'Alessio described Imperial Rome as "undoubtedly the most coveted landing place" for traders of marble keen to sell their wares in the "most flourishing market for marble" from quarries all over the Mediterranean.

As for why the lost cargo has remained at the bottom of the riverbed, D'Alessio believes it was too difficult to recover, especially considering the "impressive dimensions" of the columns.