Historians and archaeologists are trying to solve an ancient mystery that is already shedding remarkable new light on the Roman conquest of Britain.

After years of painstaking conservation work, experts at the British Museum have succeeded in reconstructing the finest Roman battle helmet ever found in the UK.

Originally discovered by a metal detectorist, as literally hundreds of corroded fragments buried in a field in the East Midlands, the helmet has gradually been revealing its secrets to British Museum conservators who have been re-assembling it like a 3D jigsaw.

In a laboratory excavation of the block of earth containing the helmet, they discovered that the front of the iron and gilt silver artefact bore a sculpture of a Roman goddess – probably Victory - and that the cheek pieces sported images of a Roman emperor and of the great classical demi-god, Hercules.

But now they are faced with solving an even more challenging mystery – who the helmet originally belonged to and the exact circumstances surrounding its burial.

Archaeologists believe that the helmet was put in the ground by native Iron Age British tribesmen as a votive offering to the gods in the months or years immediately following the Roman invasion of Britain in 43AD.

Studies of other material found at the site show that it was a major native British religious complex, used for the ritual interment of votive offerings for several hundred years – in the late Iron Age and Romano-British periods.

The investigation has so far revealed that, at around the time of the Roman conquest at least 14 other votive deposits (mostly Iron Age silver coins) were interred at the site. The helmet was also buried with native currency. In total, the original mid-first century AD value of these offerings (excluding the helmet itself) would have been the modern day equivalent of around £80,000.

But now historians are trying to place the votive offerings in the wider context of the Roman conquest itself. They are trying to unravel whether the offerings were being made to gain the gods’ support in defeating the Roman invaders – or, alternatively, to thank the gods for the arrival of the legions.

The interpretive dilemma facing historians stems from the complex nature of mid-first century AD native British politics. Historians have long known that some British tribes or sub-tribes were extremely pro-Roman at the time of the conquest – and that some others were not. However, the political position of many of the tribal kingdoms and confederacies is not yet known, including that of a people called the Corieltauvi (literally ‘the Army of the Earth Goddess’) who appear to have dominated much of the East Midlands at the time the helmet was buried.

Linked with this question of political allegiance, is the mystery of how the helmet was acquired by the native British people who buried it.

There are two main options. If those people were hostile to Rome, then it’s likely that the helmet was a war trophy, captured by Britons and buried to ensure continuing British success against the invaders. Perhaps significantly, there were parts of several other helmets buried alongside it – a fact that would be consistent with the war trophy option.

Alternatively, though less likely, the helmet could have been a diplomatic gift from a senior Roman officer to a local British chieftain – or a Roman offering at a native shrine.

But who did the helmet originally belong to? Its style shows that it was originally the property of a Roman cavalryman. He would have been a member of a cavalry unit - associated with a legion, potentially based at nearby Leicester.

Some scholars have suggested that shortly after the Roman invasion, Leicester may have become an operational base for all or part of the 14 legion (known as Gemina and originally formed a century earlier by Julius Caesar).

Some of the Roman army cavalrymen associated with that particular legion came from what is now the Netherlands – and were particularly crack troops recruited from a Germanic tribe, known as the Batavi (literally ‘the Superior Men’) – the tribal people who originally supplied the core element of the emperor’s personal mounted guards. It’s conceivable therefore that the original owner of the helmet was a Batavian, stationed in the East Midlands, but originally hailing from the Nijmegen area of the Lower Rhine.

The native British ritual site where the helmet was buried, was a large oval, possibly palisaded, complex on the summit of a hill at Hallaton, Leicestershire, overlooking the probable Iron Age ‘international’ boundary between the Corialtauvi and their southern neighbours the Catuvellauni (‘the Land of the Great Warriors’).

The earliest votive offerings – a group of gold coins of the southern British Atrebate tribe – were placed in the ground there in the late first century BC. Then, in around the 20s AD, groups of local silver coins were buried together with a small Iron Age British silver bowl, a 1.2 kilo silver ingot (made at least partly from melted-down British coins) and two continental-originating Roman glass eyes, potentially from a cult statue of some sort.

Also interred on the site was a ten pint Iron Age communal drinking vessel, the remains of a series of ritual feasts (at which around 400 suckling pigs were consumed!) – and a series of Roman brooches and a gold bracelet, buried much later in the Roman period.

The conservation and detailed analysis of the helmet, 5000 coins and other finds has taken British Museum and other experts a decade to complete since the material was originally excavated by Leicester University and a local archaeological society, the Hallaton Fieldwork Group, in 2001. The laboratory excavation and re-assembly of the helmet at the British Museum was led by one of the museum’s leading conservators, Marilyn Hockey.