The emperor Domitian was assassinated on September 18th 96AD. His wife, Domitia was amongst the plotters as was two of his Praetorian guards, Norbanus and Secundus who was the former governor of Egypt.
The populace was largely indifferent to him, the army adored him (mostly because he increased their salary) and the Senate were at once terrified and full of hatred for him and cursed his name and struck it from the records.
Domitian had his cousin Flavius Clemens executed. Clemens was ‘a man of the most contemptible sloth’ (Suetonius, Vespasian, 15) and the emperor had adopted his cousin’s sons as heirs. If Clemens could die, who else could be spared?
The charge against Clemens was ‘atheism, for which offence a number of others also, who had been carried away into Jewish customs, were condemned, some to death, others to confiscation of property’ (Cassius Dio lxvii.14).
At this point that Rome still regards Christianity as a Jewish sect (Severus, Chronicles ii.31; The lost Tacitus, Histories v). Suetonius is surely referring to Christians when he refers to Domitian exacting a tax on ‘those who lived as Jews without professing Judaism’ (Domitian 12).
It’s likely that the charge of ‘atheism’ was levelled at these people because they did not follow the ‘usual gods’, and Jews who ‘did not follow the usual gods’ are almost certainly Christians, although that term is never used specifically against them and wasn’t in use at that time.
Clemens’ wife, Flavia Domitilla, was the granddaughter of the Emperor Vespasian and hence the niece of both Domitian and his predecessor Titus. When her husband was executed, she was banished to the island of Pandateria, modern day Ventotene, off the west coast of Italy. From there, she plotted her revenge, also becoming part of the plot that to assassinate him.
Flavia Domitilla later becomes a Christian Saint and one of the earliest Christian cemeteries in Rome was the ‘Cemetery of Domitilla’, named after, and on ground owned by her. Another of Domitian’s ‘atheists’ was Acilius Glabrio, a Consul in 91. His family had a crypt in the 1st Century Christian cemetery of Priscilla.
Contrary to the popular view, that Christianity took a long time to take root in the Roman Empire, the granddaughter of the man who ultimately successfully succeeded Nero and at least two Consuls, nominally the second most powerful men in Rome, were all Christians before the end of the 1st Century.