When did the Romans try to stop the spread of Christianity?

There were some persecutions of the Christians which h were undertaken by some of the Roman emperors. They were not about stopping the spread of Christianity.
The most important persecutions were by Decius and Diocletian. Decius wanted the peoples of the empire to prove their loyalty to the Roman state by requiring them to perform sacrifices to the Roman gods (religion and the state were intertwined for the Romans). The Christians refused to do so because they considered this as a betrayal to their god and because they abhorred sacrifices. As a result they were persecuted.
The Diolcetianic persecution was prompted by a Christian criticising a sacrifice about to be performed in the imperial palace. This was considered as offending to the Roman gods. According to Lactantius a Christian writer, Diocletian and his co-emperor, Galerius discussed how to deal with the Christians. Diocletian thought that banning the Christians from the imperial bureaucracy and the army would be enough to appease the gods. Some bureaucrats and some soldiers had converted to Christianity. Galerius, who was described by Lacnatius as a crude thug and an anti-Christian, thought that the Christians were becoming arrogant and called for their extermination. The persecution policy of Diocletian was influenced by Galerius.