Emperor Constantine legalized Christianity across the Roman Empire — which sounds like a win until you look at what came next. Rome didn't convert to Christianity. It absorbed it. The imperial power structure, the hierarchy, the titles, the ceremonies — all of it got baptized and rebranded. Bishops became like governors. The Pope became like a Caesar. The church didn't transform Rome. Rome transformed the church.
Before Constantine, the church was decentralized, underground, and dangerous to belong to. After Constantine, it became the official religion of the most powerful empire on earth — with all the political machinery that entailed. That shift had consequences that are still with us.