Near the end of the third century, a new Christian movement emerged that was to have major ramifications for the history of the Christian world: monasticism. Originally, monasticism was tied to asceticism, meaning self-denial, following the example of an Egyptian holy man named Antony. In about 280, Antony sold his goods and retreated to the desert to contemplate the divine, eschewing all worldly goods in imitation of the poverty of Christ. He would have remained in obscurity except for a book about him written by a bishop named Athanasius, The Life of Antony, that celebrated Antony's rejection of the material world and embrace of divine contemplation. According to Athanasius, normal life was full of temptation, greed, and sin, and that the holiest life was thus one that rejected it completely in favor of prayer and meditation away from human company. Thousands of people followed Antony's example, retreating to the wilderness. These early monks were called Anchorites: hermits who lived in deserts, forests, or mountains away from the temptations of a normal social existence.
One particularly extreme sect of early monks were the Stylites, from the Greek word stylos, meaning "column." The founder of the group, St. Simeon the Stylite, climbed up a pillar in Syria and spent the next 30 years living on top of it. He was so famous for his holiness and endurance in the face of the obvious physical toll of living on top of a pillar that he attracted followers from all over the Roman world who came to listen to him preach. Soon, many others sought out columns in imitation of Simeon.
Ultimately, pillar-sitting did not become the predominant model of Christian life. Instead, groups of ascetics came together in communities called monasteries. Originally, these early monks spent almost all of their time in prayer, but over time most monastic communities came to embrace useful work as well as prayer and meditation. The most important development in the development of monasticism was the work of Benedict, an Italian bishop, who wrote a book known as the Rule in about 529 that laid out how monks should live. The Rule dictated a strict schedule for daily life that revolved around prayer, study, and useful work for the monastery itself (tending crops and animals, performing labor around the monastery, and so on). Going forward, many monasteries became economic powerhouses, owning large tracts of land and selling their products at a healthy profit.
More important than their economic productivity, at least from the perspective of the history of ideas, is that monasteries became the major centers of learning, especially in Western Europe after the collapse of the western Roman Empire. One of the tasks undertaken by monks was the painstaking hand-copying of books, almost all of which had to do with Christian theology (e.g. the Bible itself, commentaries from important Christian leaders, etc.), but some of which were classical Greek or Roman writings that would have otherwise been lost. Often, these books were beautifully illustrated by the monks and are referred to as illuminated manuscripts - among the finest examples of medieval art.
Outside of monasteries, churches were built in practically every city and town (and many small villages) in the Roman sphere of influence. One interesting and, from contemporary perspective, somewhat peculiar phenomenon in early Christianity was the focus on relics: holy objects. Relics were everything from the bones of saints to fragments of the "True Cross" on which Christ was crucified. Each church had to have a relic in its altar (contained in a special box called a reliquary) or it was not considered to be truly holy ground. All relics were not created equal: the larger the object, or the closer it had been to Christ Himself or the apostles, the more holy power it was believed to contain. Thus, a thriving trade in relics (plagued by counterfeits - it was not easy to determine if a given finger bone was really the finger bone of St. Mark!) developed in Europe as rival church leaders tried to secure the most powerful relic for their church. This was not just about the symbolic importance of the relics, as pilgrims would travel from all over the Roman world to visit the site of noteworthy relics, bringing with them considerable wealth - whole regional economies centered on pilgrimage sites as a result.