During the trial of Christ, Pilate, according to the gospels, wanted to free the prisoner. He was stopped by a cry that if he did so he would be no friend of Caesar's. According to commentators, Pilate recognised the threat. Every Roman governor and official was closely scrutinised by secret agents of the Emperor, 'the Agentes in Rebus', literally 'the Doers of Things'! The Roman Empire had a police force, both military and civil, though these differed from region to region, but it would be inaccurate to claim the Empire had anything akin to detectives or our own CID. Instead, the Emperor and his leading politicians paid vast sums to informers and spies. These were often difficult to control; as Walsingham, Elizabeth I's master spy, once wryly remarked, 'He wasn't too sure who his own men were working for, himself or the opposition.'

The Agentes in Rebus were a class apart amongst this horde of gossip-collectors, tale-bearers and, sometimes, very dangerous informers. The emperors used them, and their testimony could mean the end of a promising career. This certainly applied to the bloody and byzantine period at the beginning of the fourth century ad.

The Emperor Diocletian had divided the Empire into East and West. Each division had its own emperor, and a lieutenant, who took the title of Caesar. The Empire was facing economic problems and barbarian incursions. Its state religion was threatened by the thriving Christian Church, which was making its presence felt in all provinces at every level of society.

In ad 312 a young general, Constantine, supported by his mother Helena, a British-born woman who was already flirting with the Christian Church, decided to make his bid for the Empire of the West.