"Charlemagne conferred the title of Great upon himself, and posterity has ratified this title so comprehensively that it has, by a unique phenomenon, combined it with his name (Charlemagne, Carolus magnus). Caesar and Napoleon alone enjoy a fame universal as his."

The above is a quote from Henri Pirenne's A History of Europe (1936) describing the most remarkable King of the Franks whom both future French and German royal families, and many others, were eager to link to their own bloodline, several hundreds of years after his death on 28 January 814.

With some 50 major campaigns during his lifetime, Charlemagne - also known as Charles the Great or Charles I - was an acclaimed hero of the early medieval Catholic Church and played, probably, the determining role in helping Rome to break the shackles of its subordination to the Emperor in Constantinople and the Orthodox Church.

In so doing, Rome did not merely confer Charles's self-styled epithet but added another, that of new Roman Emperor, Pope Leo III using a stratagem which caused the recipient real angst at the time and which his descendants and many other European monarchs, would have cause to rue.

The Vatican, soon afterwards to become a temporal power, would all too shortly come to be embroiled in the secular power struggles and affairs other than spiritual, that has dogged the holder of the keys of St Peter ever since.

In lauding Charles in the manner he did, Leo downplayed the service and protection which Charles's father, Pepin the Short (d. 768) had given Rome in its many hours of need and more deliberately, put into the shadow the accredited saviour of Christendom, Charles's grandfather, Charles Martel (689-741).

Charles Martel – "The Hammer" – was reported by a saint of the Church soon after his death to be "writhing in the torments of hell", yet without this great leader's military and social reforms, there would never have been a Charlemagne. Why Rome's Ire?

The Merovingian Dynasty had ruled the Franks since the middle of the fifth century and under Clovis (c. 466-c511), usually described as "crafty, mean and bloodthirsty" or worse, they had, with him, converted to Christianity and the lands under their control would expand greatly to include most of Roman Gaul.

When a King died, Frankish laws of inheritance saw these lands divided amongst his sons and this invariably set brothers against each other, with the killing including all the children of the loser, needless to say.

Not helping matters was the way that each claimant to the throne gave away land as reward to their followers and to the Church and within a few generations there was little left to distribute. The Merovingians became known as "the do-nothing kings".

Trying to keep order were the Mayors of the Palace, the highest servant of the royal household, and it was these men who, whilst not having the title of King, became the de facto rulers after 640.

Charles Martel became Mayor of the Palace in 715 and is most famous for defeating the forces of the Umayyad Caliphate between Poitiers and Tours in October 732. A seasoned campaigner and disciplinarian, he saw the need to establish a permanent cavalry.

Martel gave his horsemen a large enough domain so that they could cover their costs and be ever on hand. He had created a new class: the aristocracy. Their land? Much of that had belonged to the Church and monasteries were torn down when necessary and Church funds taken to pay for his armies when the need arose, which was very often.

Whereas Charles Martel, a somewhat indifferent Christian, had the title Duke and Prince of the Franks, it would be his son Pepin the Short who would pack the last Merovingian king off to a monastery and assume the title King of the Franks in 752.

A religious man, Pepin defeated the Lombards after they threatened the Pope (Stephen) and gave the Roman See some of the towns and land of that kingdom. His devotion to the Church was a very strong influence on his son Charlemagne, who would in turn defeat the Lombards, absorbing their Kingdom and shortly after confirming the Holy See's "Donation of Pepin".

Charlemagne would famously fight the Saxons from 772 to 804, forcing them to become Christians. Undoubtedly a most Christian King himself, he had always been careful not to imply that he in any way owed his position to the Pope.

Successfully answering Leo III's plea to quell rebellion in Rome, he went to mass at Christmas 800 in the basilica of the Lateran. Approaching from behind, the Pope placed the gold Imperial crown on his head and proclaimed him to the cheering masses as Emperor – a new "Roman Empire" had been "created and granted by the hands of the successor of St Peter".

Charlemagne had been tricked and he knew very well the implications of the Pope's act. In 813, now by the standards of the time a very old man – about 70 – he himself crowned his son Louis at Aachen, denying the Pope right of sanction. Charlemagne died on 28 January 814 and soon afterwards, was buried near his favourite residence in the basilica at Aachen which he had himself built.

Charlemagne's Empire ceased to exist by 916 but the Popes would meddle in the affairs of states long after.