Monk literaly means someone who lives alone. They sought out a life completely seperate from human society in order to dedicate themselves to god. One of the first who was an example to all those who followed was Saint Anthony and prosperous Egyptian who have up all his land and went into the desert to pursue his ideal of holiness. The idea of being a monks spread rapidly and was highly popular. Soon the life of the monastic life became a communal lifestylye. The rules for that lifestyle were set by Saint Benedict of Nursia who wrote between 520-530 his rules. Under them monks primary emphasis would be on hard work and prayer.
Monastaries developed throughout Europe. The monks became the main force for conversions to Catholicism in Europe. Women also joined the monastaries as nuns and were instrumental in the conversion of Germanic kingdoms to Catholicism.