In AD 390 the Christian Roman Emperor Theodosius I was held responsible for the massacre of seven thousand people in Thessalonica in retaliation for the murder of one of his generals during a riot. When Ambrose, Bishop of Milan, learnt of the slaughter, he threatened Theodosius with excommunication, and after seven months of penance the emperor was readmitted to the pale of the church. In 1619–20 Anthony van Dyck vividly captured the bishop’s power in a painting that showed Ambrose barring Theodosius from entering the cathedral at Milan.

Christianity had come a long way since the first century AD. Christians’ strict belief in their God forbade them from making sacrifices to the emperor and the pagan gods. In the early days they tended not to participate in public life, and could