Constantine the Great was considered one of the greatest emperors of the Roman Empire. Elizabeth Hartley looks back at his life -1700 years after he was first proclaimed emperor by his troops.

THE story of Constantine the Great began in York. Had he not been in York with his father, the emperor Constantius, on July 25, 306, when the latter died, he would not have been handed the greatest prize - the right of succession to his father's title.

Although we do not know exactly what happened on that day, it is clear that Constantine was extremely well prepared for the role he was taking on and he seized the opportunity offered him by fate in York.

Constantine's father had been promoted to the position of Caesar, a junior member in the imperial college, in 293 when Constantine would have been just over 20. This elevation ensured his son a place at the imperial court. But it was not his father's court at Trier, Germany, that Constantine joined, but that of the senior emperor, Diocletian, based principally at Nicomedia, in present-day Turkey.

Here, he would have received the training suitable for an imperial heir. He was taught rhetoric by the well-known Latin orator and poet Lactantius, campaigned with Galerius in Mesopotamia, and travelled with Diocletian through Palestine and Egypt, and probably even to Rome.

Thus trained for high office with the skills of both statesman and soldier, Constantine was fully prepared to seize the opportunity offered to him in York in 306.

Six years later and Constantine had a battle to fight. Maxentius, a usurper, seized power in Rome and, following several unsuccessful attempts by other emperors to overthrow him, Constantine was victorious at the battle of Milvian Bridge and marched into Rome. He attributed his success to divine favour following his decision to embrace the Christian faith just before the battle.

It is said that he saw a vision of the Chi Rho in the sky, the Christian symbol which combined the Greek letters Chi and Rho (which look like our letters X and P) and ordered his soldiers to mark shields with the letters following his victory.

Against this background, it is interesting to consider the extent to which Constantine's proclamation in York might have affected the city. York, legionary fortress, colonia, and capital of Lower Britain for 100 years, had become the capital of one of four provinces which made up the Diocese of the Britains in 296. This province was most likely known as Flavia Caesariensis, and hence named after Constantine's father Flavius Constantius as Caesar. It therefore seems no accident that the larger-than-life-size marble head of Constantine should have been discovered in York in the area of the fortress near the headquarters building.

The hall of the headquarters building was rebuilt under Constantius or Constantine and a statue of Constantine is likely to have been placed there. There are also still standing the monumental remains of the corner-tower of the fortress with its connecting curtain wall, which fronted the river. The magnificence and sheer scale of this frontage when complete suggest that it was built with imperial backing, suitable for the high status of York and its position as a place where emperors resided and major events took place.

The closest we can get to the power of Constantine is through such imperial images and monuments. From Trier, the afterglow of imperial splendour can be felt through the remains of his great audience hall, the Aula Palatina. From Rome, Constantine's colossal marble head; the bays and apse of his Basilica, and his magnificent arch alongside the Colosseum in Rome are lasting tributes to his power.

The personal effects of Constantine and his family, such as regalia, jewellery and arms and armour do not survive. But associated with the emperors Constantius and Constantine are high-quality gifts, produced for those in their entourage and supporters, both civilian and military.

Many of these gifts, given as public displays of largess, were inscribed with the name of the emperor or displayed his portrait. Among the items that survive are jewellery, medallions and plates.

For Constantine, July 25 became his 'day of power' (dies imperii), his accession day celebrated annually, although with special magnificence at the opening and closing of the fifth, 10th, 20th and 30th years of his reign. On each occasion, there would have been great processions of the emperor and his family, speeches, chariot races in the circus and the dedication of buildings, statues and monuments.

The Arch of Constantine was dedicated in 315 during his visit to Rome for the start of his 10th-year celebrations.

Although we lack details of Constantine's visits to Britain after his initial accession, coin evidence does suggest that he was there on more than one occasion during his first ten years in power. Almost certainly, York would have been one of the places to experience again an imperial adventus (arrival) and period of residence of emperor and court.

What effect his elevation in York had on Britannia as a whole we will never know. However, major finds in Britain provide evidence of the great wealth and prosperity sustained through the peace brought to the province by Constantius and Constantine.

The prosperity and stability evident in Britain and elsewhere throughout the empire at this time reflect the strength of leadership, commitment and vision of Constantine. He was emperor for 31 years, until his death in 337, and the longest serving emperor since Augustus, the first of the Roman emperors.

Constantine chose to reinvigorate his empire by looking back to the imagery and artistic tradition of the age of Augustus.

Later, he also looked back to the other great figure of the classical past, Alexander the Great. By choosing to model himself first on Augustus and then Alexander, Constantine was clearly expressing an image of his own destiny: he would be one of the great figures of history who would be remembered for all time.

With this sense of history and his role within it, Constantine moved with some caution during his long reign, being careful not to enforce sudden change and mindful to foster tolerance of belief. He legitimised Christianity and ordered the building of churches in Rome - including St Peter's at the heart of today's Vatican City - and elsewhere, while allowing Judaism to be tolerated and paganism, with modifications, to continue. Constantine played an active part in creating a golden age throughout the empire.

The exhibition at the York Museums Trust looks as the late Roman Empire from a cultural point of view. It focuses on the art, with its richness of colour, texture and materials, and includes finely carved sculptures and cameos, medallions and decorated silver plate, brilliantly coloured textiles and paintings and mosaics. The exhibition also takes full cognisance of all aspects of religious activity of the period. This massive cultural achievement and legacy could not have been possible without Constantine.

In 324, Constantine defeated Licinius, emperor of the east, and Constantine became sole Roman emperor. He created a New Rome at the Greek city of Byzantium and built a palace and several major churches. The city was officially renamed Constantinople in 330.

Constantine died in 337, aged 87, and was buried in the Church of the Holy Apostles in Constantinople, now Istanbul. His ability and vision reshaped the world in which we live.

* Elizabeth Hartley is curator of the Constantine exhibition which runs at the Yorkshire Museum, in York, until October 29. There will be a service at York Minster at 3pm today to commemorate Constantine's accession followed by a procession to the Yorkshire Museum gardens.