Along with this push for consistency from Theodosius (called "the Great") came a shift away from tolerating all religions. Anti-pagan laws existed (that is, those religions that did not follow the Greco-Roman gods), but there is no record of them actually being enforced. Theodosius declared Nicene Christianity the official religion of the empire, but this was mostly an attempt to stamp out the "heresy" of Arianism.
Animal sacrifice was a chief target of Christians' demand for legal changes. Altars for blood sacrifice—a central practice of pagan ritual since pre-history—were routinely smashed. Eliminating it was a primary goal of Christians who were gaining political influence. This change had started prior to Theodosius: the Emperor Julian (reigned 360-363) was pagan, but when he restored pagan altars in Antioch, Christians destroyed them again. Christians were still a minority, but they were making themselves known.
Theodosius did not want open rebellion against his decisions, so pagan temples were allowed to remain open, and worship could take place. Pagan holidays could be celebrated, but they were no longer days off from work. Animal sacrifice and divination were banned. Theodosius' praetorian prefect, Maternus Cynegius, took it upon himself to vandalize pagan shrines in the eastern provinces. When he died, however, Theodosius replaced him with a moderate pagan who offered more protection to pagan temples. The emperor also named pagans in the senate to important administrative posts.
Not all temples were destroyed; it is likely that some were converted to churches. Modern archaeology has found evidence of 120 churches that started as pagan temples. Of course, 120 out of the thousands that would have existed in the empire is not a significant percentage.
The sack of Rome by Visigoths in 410 was a shocking moment for the empire, and pagans blamed the shift to Christianity as the source of a weakened empire. This prompted Augustine of Hippo to write the work we know as The City of God, except that was not what he called it. Augustine called it De civitate Dei contra paganos, "On the City of God Against the Pagans," which would set the tone of anti-pagan thought for centuries. What he meant by that will be tomorrow's post.