Monks and missionaries traveled through countries such as britain, ireland, and countries in Northern Europe spreading Christianity.
By the time the Roman Empire collapsed, Christianity began spreading throughout Europe, primarily through the efforts of monks and missionaries.
Spreading Christianity was a slowly process. It took time for the religion to reach numerous places and to be adopted by local people. In Europe, Christianity began as an urban religion. It spread to wealthy landowners and then to rural tenant farmers. Meanwhile, missionaries focused their efforts on noblemen.