A fragment of an ancient Roman equestrian statue that once adorned the Colosseum has been found during excavations near the world famous Italian landmark.

According to the Italian daily, Il Messaggero, the fragment was discovered among the remains of an ancient pavement that once surrounded the amphitheatre.

"A marble fragment measuring one metre by a metre and a half, is from an equestrian statue, probably a statue that embellished the arches of the Colosseum," said archaeologist Silvana Rizzo, advisor to the minister of culture and tourism, Francesco Rutelli.

"The left flank of a rider with the detail of a leg, bridle and harness of a horse, as well as a part of a dagger scabbard are perfectly visible from the fragment," said Rizzo, who has spent his life doing Roman excavations.

"They are details that suggest the statue of an emperor and left us with the hope that we could find the entire statue."

According to Il Messaggero, the archeological find is a reminder of how many pieces of ancient sculpture are discovered on a regular basis in the Italian capital when centimetres of soil are swept away.

Angelo Bottini, Rome's archeological superintendent, called the discovery of the equestrian statue "an exceptional discovery".

"What's clear is this new discovery is the umpteenth demonstration of the underground surprises in Rome that are a gift to us," Bottini told the Italian daily.

The new discovery could shed light on the statues that once adorned the exterior wall of the Colosseum.

The Colosseum, also known as the Flavian Amphitheatre, was constructed by the Emperor Vespasian in 72 A.D. and inaugurated by his son Titus in 80 A.D.

It was the largest amphitheatre ever built in the Roman Empire and considered one of the greatest examples of Roman architecture and engineering.

But it has suffered extensive damage over the centuries due to earthquakes and pillaging.

The arches on the third floor of the Colosseum were decorated by three eagles, signs of power in Rome, while the second floor had statues of ancient gods, Hercules, Apollo and Aesculapius.

Experts believe the uncovered equestrian fragment could have been part of a statue above the Imperial entrance to the amphitheatre.

More archaeological discoveries are expected to be uncovered as the city proceeds with construction of its third subway line near the Roman Forum, in the heart of the Italian capital.

Construction on the 30-station line has already been interrupted several times as archeologists have uncovered ancient and mediaeval treasures.

Under Italy's strict conservation laws, the city must decide whether any historic objects are removed or preserved.

The 4.6 billion dollar subway line is expected to be completed in 2015.