The transition from paganism to Christianity in the Roman Empire and beyond was a complex process that unfolded over several centuries, involving a mixture of political, social, and religious changes. It wasn’t so much that Christianity “destroyed” paganism, but rather that it gradually became the dominant religion through a series of developments. Key factors in this transition included:

1. Legal and Political Support: The turning point for Christianity came with the conversion of Emperor Constantine the Great to Christianity in the early 4th century AD, after which he began to support the Christian Church politically and financially. The Edict of Milan in 313 AD granted religious tolerance for Christianity, and subsequent laws and edicts favored Christianity over pagan religions.
2. Imperial Patronage: Following Constantine, subsequent Roman emperors, with few exceptions, were Christians and continued to promote Christianity through building projects (such as churches), grants, and preferential treatment for Christian clergy. This imperial patronage significantly boosted the prestige and influence of Christianity.
3. Legislation Against Pagan Practices: Over time, laws were enacted that restricted pagan practices. For example, sacrifices and divination were outlawed, and temples were closed or repurposed for Christian use. These laws varied in their enforcement and impact but cumulatively contributed to the decline of traditional pagan practices.
4. Conversion Efforts: Missionaries played a crucial role in spreading Christianity among the population, often adapting Christian practices to local traditions and thereby making the new religion more appealing. Over time, as more people converted to Christianity, the social and political influence of pagan practices and practitioners waned.
5. Socio-Economic Factors: Conversion to Christianity could offer social and economic advantages, particularly as the religion gained favor with the ruling elite. This sometimes led communities or influential individuals to convert, further diminishing the public role of paganism.
6. Syncretism: In many instances, the transition from paganism to Christianity was not abrupt but involved the blending of pagan and Christian practices and beliefs. Christian holidays were often aligned with pagan festivals, and Christian saints sometimes took on roles similar to those of pagan gods, easing the transition for converts.

It is important to note that the decline of paganism was not uniform across the Roman Empire or beyond, and it persisted in various forms for centuries in some regions. Rural areas, in particular, held onto pagan traditions longer than urban centers. The process was gradual, complex, and varied greatly from place to place.

In summary, the shift from paganism to Christianity in the Roman Empire and its territories was a multifaceted process influenced by political, legal, and social changes, rather than a single event or a straightforward case of one religion destroying another.