The title Imperial Church is given to the period of time between the regular but not consistent persecution of the church and the beginning of the middle ages.  

The not so friendly notion of this time is it is when the Church got so connected to the empire that it was hard to tell the difference between the two. (This uncomfortable alliance ran through the Reformation and is with us today in many quarters.) For the Imperial Church to rise the Empire had to first recognize and then appropriate Christianity. This began to happen with the 'conversion' of Constantine in 312. With the edict of tolleration, persecution that had been common but not constant ended oficially. Communication between Christian centers improved and the Church began to have discussions on many theological matters prompted in no small part by the political powers of the day. The Emperor wanted a unified Christianity if Christianity was to be his banner and the church was trying to sort out one important issue: "what exactly it means for God to have a son."

Especially in Protestant circles, it is popular to say that this was the time that Christianity really got messed up combining with the trappings of paganism and the state. This time is also far enough removed in time from the life and ministry of Jesus for people to question just what the message of the Gospel was.  We see the Christological divisions that started with in New Testament times continuing through this period with the Emperor siding with various factions at various times. 

Date Comment
310 - 390 Apollinaris, begins to teach that Jesus had a human body but not a human mind; He had the divine mind.  This is sometimes known as a Word-Flesh Christology in which the divine Word occupies the human Christ. Gregory of Nazianzus' reply: "What has not been assumed cannot be restored; it is what is united with God that is saved." The orthodox position being that Christ as god assumed human nature.
310 – 383 Ulfilas, bishop, missionary, and Bible translator during the peak of Arian controversy. He is credited with the first translation of the Bible into a Germanic language. He is thought by most to have had an Arian christology.
311 Edict of Toleration ends official persecution of Christians.
312 Constantine defeats Maxentius at the battle of Milvian Bridge and becomes Emperor of the West. Constantine had had a vision, and used the letters chi and rho (the first two letters in "Christ") as his symbol during the battle. This event marked the beginning of his 'conversion.'
312 Caecilian elected bishop of Carthage. He was lax toward the Traditores. And he seemed unenthusiastic about the martyrs. A group in Carthage rejected Caecilian's election on the grounds that he was ordained by a traditore. They elected a rival bishop named Majorinus.
313 Edict of Milan gives Christians equal rights. (Legalizes Christianity.) It is issued by Constantine in the West and Licinius in the East, but Licinius soon withdraws his commitment to it.
314 By this date, there is a significant number of Christians in Britain.
315  Majorinus dies, Donatus is his successor. This party becomes known as the Donatist party or even a schismatic group.  They insisted that the church must be pure and that the sacraments administratered by the clergy who had not resisted the Dioclesian persecution were invallid.
316 The Donatists appeal to Constantine, but he rules against them. Then he outlawed them and banished them in an effort to unite the church.
316 - 397 Martin of Tours.
324 Constantine defeats Licinius and becomes Emperor of both East and West. Constantine favored Christianity, which strengthened its position in the empire.
325 Council of Nicea condemns Arianism. Arius, in Alexandria, taught that Christ was the first created being, that there was a time when He was not. The council declared that Jesus was begotten, not made, and that He is Homoousios, of the same substance as the Father.
328 Athanasius becomes bishop of Alexandria.
328 Constantine revokes the sentence against Arius
329 - 379 Basil the Great.  He is the monk who created the basic Rule for the Eastern Orthodox monks that is still in use today. Basil taught communal monasticism that serves the poor, sick, and needy. (One immediate effect of the disappearance of persecution is the rise of monasticism to replace the old martyr witness.)
337 Death of Constantine - left empire to his sons.
338 - 397 Ambrose the Churchman, who fought Arianism and the revival of paganism, and promoted the power of the Church.
340 - 380 The Arian Controversy
340 Eusebius of Caesarea, the Church Historian dies.
340 Ulfilas converted to Arian Christianity. He takes it to the Germanic tribes, gives them an alphabet, and translates the Bible into their language. Most of the Germanic tribes became Arian Christians
347 - 407 John Chrysostom, "Golden Mouthed." He was a bold and reforming preacher, who used the Historical-grammatical method of exegesis. This was unusual, because exegetes had been looking at the allegorical interpretation ever since Clement of Alexandria and Origen.
292 –348 Pachomius - founder of Christian cenobitic monasticism.  That is monasticism that focuses on community life rather than the live of a hermit as with the Desert Fathers.
347 - 420 Jerome, the great Bible scholar and translator of the Vulgate
351 - 356 Anthony of Egypt
353 Emperor Constantius begins his pro-Arian campaign and drives Athanasius from Alexandria
354 - 430 Augustine
361-363 Reign of Julian the Apostate, Roman Emperor who converted from Christianity to paganism and restored paganism in Rome
361 Julian the Apostate removes the restrictions against the Donatists
369 Pelagius (354-440), said to have originated Pelagianism.
367 A letter of Athanasius names the 66 books of the canon.
379-395 The reign of Theodosius, who establishes Christianity as the official religion of the Roman Empire
380 Edictum de Fide Catholica establishes Christianity as the state religion of Rome.
381 Council of Constantinople. The Nicene position becomes dominant again, and the legal religion of the Empire.  Jesus Christ is truly human, contrary to Apollinarianism, which held that Jesus had a human body but a divine mind. The Great Cappadocians are the inspiration behind the defeat of Arianism at this council.
382 A council in Rome affirms the authority of the New Testament canon. It is important to remember that the content of the canon was not really a decision of this council. The Roman Church formally recognized the canon at this point. 
386 Augustine was converted in a garden in Milan after hearing a child saying "Take up and read!" He took up Romans 13: 13-14.
387 Augustine baptized by Ambrose
c. 389 St. Patrick. He was a British Romanized Christian who established Christianity in Ireland.
391 Augustine ordained a priest in Hippo, North Africa
393 The Council of Hippo recognizes the canon. To be recognized as canonical, a book had to be Apostolic, fit in with the other scriptures, and have been of fruitful use throughout the church up to that time
395 Augustine becomes bishop of Hippo
397 The Council of Carthage agrees with the Council of Hippo
397-401 Augustine writes Confessions
440-461 Papacy of Leo the Great. He was influential at Chalcedon. He also argued for papal supremacy and showed political leadership in his negotiations with Attila the Hun. There are many who say that he is the first Pope in the modern sense and the first to claim papal succession back to Peter.
398 John Chrysostom becomes bishop of Constantinople
410 The Fall of Rome to Alaric and the Visigoths
411-430 Augustine's Anti-Pelagian writings. Pelagius rejected the idea that we all fell in Adam (Federal Headship), original sin, and the sin nature. We could earn our salvation by works, so grace is not necessary. Augustine insisted that we all sinned in Adam, and spiritual death, guilt, and our diseased nature is the result. God's grace is necessary not only for us to be able to choose to obey God's commands, but to be able to choose to turn to God initially for salvation.
413-426 Augustine writes The City of God. Some people blamed the fall of Rome on the Christians, saying it happened because Rome abandoned paganism. This is Augustine's response, along with many diversions.
418 The Council of Carthage anathematized the teachings of Pelagius.
429 Arian Vandals cross into Africa. After this, Western Emperors became puppets of Germanic generals.
431 Council of Ephesus. Jesus Christ is one person, contrary to Nestorianism, which held that Christ was two persons, one divine and one human.
445 Valentinian III - Decree on Papal Power
448 Leo writes an epistle to Flavian, The Tome of Leo, to encourage him. It encapsulates the Christology of the church, drawing from Augustine and Tertullian.
449 The Latrocinium (Robber's) Council. Dioscorus, Patriarch of Alexandria, presided. This Council declared Eutychianism, which held that Christ had only one nature, to be orthodox. According to this heresy, His humanity was not like ours. This would make redemption impossible. The council deposed Flavian, the orthodox Patriarch of Constantinople.
451 Council of Chalcedon. Eutychianism is condemned, Dioscorus is deposed, The Tome of Leo is confirmed. Jesus Christ is "two natures, the Divine of the same substance as the Father (against Arianism), the human of the same substance as us (against Eutychianism), which are united unconfusedly, unchangeably, indivisibly, inseparably (against Nestorianism)." The church remains divided over these issues for the next 200 years
476 The last Emperor, Romulus Augustulus, is deposed by Odoacer, a German general - This marks the end of the Roman Empire in the west.

 

Based on: http://www.churchtimeline.com/imperial.htm  8/8/11