Hundreds of Roman statues that make up the world's greatest private collection of its kind are to be put on public display in Rome after spending more than 40 years in storage.

The Torlonia Statues are considered priceless, but their owners have now agreed to sell them to the city for £100 million.

The collection is named after the aristocratic Roman family that acquired it almost two centuries ago as security for a loan it made to another dynasty, the Giustiniani family, who then defaulted.

It comprises 620 marble and alabaster statues and sarcophagi from the Roman empire, including busts of Julius Caesar, sculptures of the ancient gods and Roman copies of Greek statues.

After long refusing to part with its treasures, the Torlonia family is said to have reconsidered the offer by the city. Sources close to the talks said a blueprint agreement had been reached in the past few days between the family, city hall, and the Fondazione Casse di Risparmio di Roma, a private banking foundation that had in turn enlisted other banks to raise the money. It is hoped that a formal agreement will be signed next month.

The Torlonia collection was consigned by the family to storage in the early 1960s, since then it has never been seen by the public. The purpose was to enable the family's stately residence-cum-museum on Rome's Via Lungara to be transformed into 93 flats.

Until now, however, the family has resisted numerous calls to part with the collection, saying that it intended eventually to exhibit the statues at its Villa Albani in Rome.

But planning permission for a purpose-built gallery which the family wanted to construct in its grounds, together with a multi-storey car park, was never forthcoming.

Three years ago, Rome's mayor, Walter Veltroni, offered the family the palace on Via dei Cerchi, which is presently used to house municipal offices.

The following year, Silvio Berlusconi, Italy's billionaire prime minister, was said to have offered to buy the collection in order to donate it to the state. But the idea came to nothing.