The head of the ancient king who commissioned one of Rome's most famous statues has gone on show for the first time in Italy.

Many people believe the Dying Gaul in Rome's Capitoline Museums celebrates a Roman conquest, but it was actually commissioned by Attalus I (269-197 BC), first king of Pergamon in modern-day Turkey.

The statue commemorates Attalus's triumphant victory over a Gallic tribe known as the Galatians in 238 BC.

The head of Attalus I and that of the last king of Pergamon, Attalus III (170-133 BC), have been loaned by state museums in Berlin and are on display in Rome's Palazzo Massimo alle Terme.

Both heads were dug up by German archaeologists during excavations at Pergamon in the second half of the 19th century and are thought once to have belonged to larger-than-life statues of the rulers.

Dated to the third century BC, the head of Attalus I is topped by a mass of short wavy curls, but according to Perugia University archaeologist Filippo Coarelli the hair is not the king's own. In the ancient equivalent of a PR job, a wig' of curls was added to the statue at a later date to make the ruler look more like Greek golden boy Alexander the Great.

Initially the governor of Pergamon, Attalus I set the Attalid dynasty rolling when he crowned himself king of the city following his victory over the Galatians.

The king was worshipped as a hero after his death, and experts believe his marble head was given the new hair-do at the beginning of the second century.

''It's one of the most extraordinary and skilful pieces from the little-known period that marked the beginning of the Hellenistic age,'' said Coarelli, explaining that there is a lack of historical documentation for the time. ''Many of the works from this period are difficult to date - but not so for this head, which is a chronological cornerstone,'' he added.

Carved between 138 and 133 BC, the head of Attalus III is more classically styled and has a brooding look. It was found in a small Greek temple on a podium at the foot of the Theatre of Pergamon. A staunch supporter of the Roman Empire, Attalus III had no heirs and bequeathed the city of Pergamon to Rome on his death in 133 BC, ending the Attalid dynasty.

The heads are on loan as part of an agreement between Italy and Germany that will also see the two countries cooperating in research, restoration and the preservation of archaeological sites. In return, Italy has lent Berlin the famous bronze Boxer, a statue dating back to the first century BC that was found on the Quirinale hill in the 19th century, where it may once have decorated the Baths of Constantine. The Boxer usually forms part of the permanent collection at Palazzo Massimo, where the Attalid heads will be on show until 16 March.