NEXT time you're walking along Rougier Street, it might be worth pausing for a moment to think about what lies beneath. Because chances are that you might just be following in the footsteps of a Roman emperor or two.

Somewhere hereabouts there may well once have a been a Roman Imperial palace.

We don't know exactly where, admits Ian Milsted of the York Archaeological Trust.

But at least two Roman emperors once based themselves in York for a while: the Emperor Septimius Severus from 208-211 AD, and the Emperor Constantine, who was almost certainly proclaimed emperor here in 306 AD.

York then was at the very farthest northern edge of empire, Ian says. "It was 'here be dragons' territory. But if the emperor came here, and spent time here, there has to have been somewhere for him to live."

Severus based himself here while leading campaigns against the Caledonians north of Hadrian's wall, who had been attacking targets in the north of Roman Britain. But while he was here the vast Roman empire was effectively governed from York - or Eboracum, as the Romans knew it.

Severus, known as the 'African Emperor' because he had been born in Libya, is though to have brought a huge retinue of civil servants and soldiers with him.

But if there was an 'imperial palace' to house the emperor and his retinue, where was it? The simple answer is that we don't know, Ian admits: except that it wouldn't have been too close to the river, and would likely have been on slightly higher ground.

So what do we know about Roman York?

The Roman Ninth Legion, an army unit of about 5,200 men, arrived here in 71 AD and founded a fortress. Fifty years later, in about 120 AD, it was replaced by the Sixth Legion, which helped with the building of Hadrian's Wall.

The fortress remained an important army base until the Romans left York in about 410 AD. And at some point during the centuries of Roman occupation, a civilian settlement began to grow up on the opposite, south-western bank of the river. It was linked to the fortress on the other side of the river (which in Roman times was much wider and shallower than now, but also tidal) by a bridge.

The civilian settlement gradually grew in size and importance until, some time after 200 AD (possibly after Septimius Severus had set up his court here), it was granted the status of 'colonia' - the highest rank of Roman city.

Evidence of the Roman presence in York all those centuries ago is all around us beneath our feet.

We know where the Roman fortress was - on the east side of the river, centred on the area where the Minster stands today, and occupying a large diagonal space stretching from the corner of Lord Mayor's Walk and Gillygate to the Multangular Tower in Museum Gardens, then down parallel with the River Ouse to Jubbergate and up to the Merchant Taylor's Hall.

We also know the rough extent of the civilian city, or colonia, on the other bank of the River Ouse - it was centred around present-day Rougier Street, North Street and George Hudson Street. And archaeologist have unearthed some tantalising glimpses of what the colonia might have been like

Previous digs have revealed evidence of some kind of Roman public building - possibly a baths or temple - under what is now the Aviva building; what may have been a bridge head for the Roman bridge, also near the Aviva building; a cluster of temples around what is now Micklegate; and numerous Roman cemeteries, including under what is now the Mount and the railway station. These would have lined the Roman road to Calcaria (Tadcaster) outside the city limits of the Roman colonia.

There seems to have been some kind of terracing of the south bank of the Ouse near Skeldergate in Roman times. and archaeologists have also discovered traces of Roman water pipes. "So there must have been an aquaduct," Ian says. "Though probably not a big, arched one."

We also think there might well have been a gladiatorial arena somewhere: dozens of skeletons of young men from Roman times which were dug up on Driffield Terrace some years ago carried evidence of injuries which suggested they may have been gladiators. "So we assume there was an arena somewhere," says Ian.

But there's still so much that we don't know. We don't know where the Forum (the central square surrounded by administrative buildings) was; or where the palace was, assuming there was one. We don't even know the size of the civilian city - or where its precise limits lay.

All we really have are a few pieces of the jigsaw, Ian says. "We've only seen a tiny fraction of the Roman city - perhaps about three per cent. We don't know where the major public buildings were, where the food came from, where the aquaduct was, how many people were here."

That's why the York Archaeological Trust is so excited about plans for a £150 million redevelopment on Rougier Street.

Under the proposals, three buildings - the Society Bar, Rougier House and Northern House - will be demolished to make way for a new hotel, up to 228 flats, plus offices, cafés, shops and restaurants.

But crucially, included in the plans is a proposal for a new, multi-million-pound Roman attraction underground beneath the Society Bar. The attraction will be modelled on Jorvik, the famous Viking museum at Coppergate - but will be twice the size.

Before all of this, however, there will be a 'once in a generation' archaeological dig, similar to the Coppergate dig of the 1970s which led to the development of Jorvik.

The aim of the two-year dig - which all being well will start next summer - will be to find out as much about the Roman colonia as possible. And the new Roman museum will be very much shaped by what is found, says Ian. Like Jorvik, it will be an underground attraction created on the actual site of the Roman evidence uncovered during the dig.

So what do archaeologists hope they may find?

Well, in addition to evidence of public buildings, Roman roads and public squares, they think they just might uncover something far more elusive: evidence of the daily lives of ordinary Romans.

One of the great things about the Coppergate dig was that the damp, peaty soil preserved things - wood, leather, cloth fabric, crops, even a piece of Viking poo - that gave a real insight into the everyday lives of the Vikings: what they wore, what they ate, how skilled they were as craftsmen and women, even what diseases they suffered from.

The hope is that the waterlogged soil beneath Rougier Street might yield some similar evidence about the lives of ordinary Romans - bringing us closer to them than ever before.

"The wet ground can preserve artefacts that would normally disappear," Ian says.

A bit of Roman poo beneath Rougier Street? Now that would be a find...

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Provided the plans for the Rougier Street development go through, the two-year Roman dig (which the York Archaeological Trust says will be 'one of the largest of its kind in the UK' - could start as early as next summer.

The plans are to make it as accessible as possible - and to get the people of York involved, says Ian Milsted, the York Archaeological Trust's head of archaeology.

There will be a viewing gallery from which spectators can watch the dig in progress, and opportunities for volunteers to take part in the dig.

There are also plans for a major schools educational programme. "We want every schoolchild in York and Yorkshire to see the dig, either physically or virtually," Ian says.

Watch this space...

To find out more about the Roman dig, and to sign up for alerts about events or volunteering opportunities related to it, visit digforeboracum.co.uk