Old Testament precedents include the Nazirites, the Essenes, the companies of prophets, and desert-dwelling prophets like Elijah.
~1 A.D. - St. Anna the Prophetess is described by St. Luke as follows: “[S]he was of a great age, having lived with her husband seven years from her virginity, and as a widow till she was eighty-four. She did not depart from the temple, worshiping with fasting and prayer night and day.” (Luke 2:36-37) Luke’s description goes on to give evidence of her faith in Christ in Luke 2:38, thus making her perhaps the first Christian to live a monastic life.
~20 A.D. - St. John the Baptist may be the earliest monk-like figure in the New Testament, because he lived in the desert for most of his life (Luke 1:80) while adopting the lifestyle of a hermit (Matthew 3:4, Luke 1:15).
~30 A.D. - Jesus promoted the model that monks and nuns would adopt in several ways. Living in the desert for 40 days (Matthew 4:1-2), promoting celibacy for the kingdom of God (Matthew 19:12), telling his disciples that they will be blessed for leaving wives and family and following Him (Luke 18:28-30), and revealing the evangelical counsels of poverty (Matthew 19:21), chastity, and obedience (Matthew 6:24) were some of the ways He promoted the monastic tradition.
~66 A.D. - St. Paul - “Honor widows who are real widows. … She who is a real widow, and is left all alone, has set her hope on God and continues in supplications and prayers night and day… Let a widow be enrolled if she…[has] devoted [herself] to doing good in every way. But refuse to enrol younger widows; for when they grow wanton against Christ they desire to marry, and so they incur condemnation for having violated their first pledge. … [And] let the church…assist those who are real widows.” (1 Timothy 5:11-16)
~95 A.D. - St. John - The Book of Revelation assigns a special place in heaven to lifelong virgins, which is a characteristic of monks and nuns: Revelation 14:4.
107 A.D. - St. Ignatius of Antioch - “I salute…the virgins who are called widows. Be strong, I pray, in the power of the Holy Ghost.” (Letter to the Smyrnaeans Chapter 13)
151 A.D. - St. Justin Martyr - “And many, both men and women, who have been Christ’s disciples from childhood, remain pure at the age of sixty or seventy years; and I boast that I could produce such from every race of men. For what shall I say, too, of the countless multitude of those who have reformed intemperate habits, and learned these things? For Christ called not the just nor the chaste to repentance, but the ungodly, and the licentious, and the unjust; His words being, I came not to call the righteous, but sinners to repentance.” (First Apology Chapter 15)
And: “[E]ven [some women] who are not barren abstain from sexual intercourse, some being virgins from the first, and others from a certain time. And we see men also keeping themselves virgins, some from the first, and some from a certain time.” (On the Resurrection Chapter 3)
160 A.D. - Acts of Paul and Thecla - “At length, certain gentlewomen hearing of the virgin Thecla, went to her, and were instructed by her in the oracles of God, and many of them abandoned this world, and led a monastic life with her.”
177 A.D. - Athenagoras - “Nay, you would find many among us, both men and women, growing old unmarried, in hope of living in closer communion with God. [For] remaining in virginity and in the state of an eunuch brings [a person] nearer to God.” (Plea for the Christians Chapter 33)
195 A.D. - St. Clement of Alexandria - “[All who] endeavour to be assimilated to the [image] given by [God], strive, from exercise, to become free of concupiscence. For he who has exercised concupiscence and then restrained himself, is like a widow who becomes again a virgin by continence. … Such are the [spiritually elevated] souls, which the Gospel likened to the consecrated virgins who wait for the Lord.” (Stromata Book 7 Chapter 12)
~250 A.D. - St. Paul of Thebes - During the persecution by Emperor Decius, Christian hermits grew in numbers as monks fled to the desert. This started the movement known to historians as the Desert Fathers, who drew inspiration from Elijah and St. John the Baptist. An early example was St. Paul of Thebes, whose decision to become a hermit is described in St. Jerome’s Life of Paulus:
“During the persecutions of Decius and Valerian…Paul [of Thebes]…retired to a house at a considerable distance [from the town] and in a more secluded spot. … [Later he] fled to the mountain wilds to wait for the end of the persecution. He began with easy stages, and repeated halts, to advance into the desert. At length he found a rocky mountain, at the foot of which, closed by a stone, was a cave of no great size…and there in prayer and solitude [he] spent all the rest of his life.” (Life of Paulus Paragraphs 2-6)
~271 A.D. - St. Anthony of the Desert’s decision to live a monastic life in the desert is described in his biography by St. Athanasius:
“[T]here were not yet [very] many monasteries in Egypt, and no monk at all knew of the distant desert; but all who wished to give heed to themselves practised the discipline in solitude near their own village. … [Anthony] hurried to the mountain…found a fort, so long deserted that it was full of creeping things…crossed over to it and dwelt there. … [And] it happened in the end that [more] cells arose even in the mountains, and the desert was colonised by monks, who came forth from their own people, and enrolled themselves for the citizenship in the heavens.” (Life of St. Anthony Paragraphs 3, 12, 14)