Edward Gibbon (The Decline and Fall of the Roman Empire) suggested that Constantine's conversion of himself and his subjects to Christianity was one of the principal causes of the fall of the western Roman Empire, which ceased to exist 139 years after his death. Michael Grant (The Emperor Constantine) agrees that Christianisation may have accelerated the process, but is less certain about the importance of this one factor, placing greater emphasis on other policies of Constantine.

The Christian policy of destroying all books that did not benefit Christianity, even the Great Library of Alexandria, and of restricting education to the clergy, brought about a sudden loss of knowledge and intellectual skills in the empire, and contributed to the onset of the Dark Ages. Many of the technological developments of the early Roman Empire were not recreated until a thousand years later.

The first known use of plenary indulgences was in 1095 when Pope Urban II remitted all penance of persons who participated in the crusades and who confessed their sins. Later, the indulgences were also offered to those who couldn't go on the Crusades but offered cash contributions to the effort instead. In the early 1200s, the Church began claiming that it had a "treasury" of indulgences (consisting of the merits of Christ and the saints) that it could dispense in ways that promoted the Church and its mission. In a decretal issued in 1343, Pope Clement VI declared, "The merits of Christ are a treasure of indulgences." (c)

See the related link.

During the persecutions, those Christians who had fallen away but desired to be restored to the communion of the Church often obtained from the martyrs a memorial (libellus pacis) to be presented to the bishop, that he, in consideration of the martyrs' sufferings, might admit the penitents to absolution, thereby releasing them from the punishment they had incurred. Tertullian refers to this when he says (To the Martyrs 1): "Which peace some, not having it in the Church, are accustomed to beg from the martyrs in prison; and therefore you should possess and cherish and preserve it in you that so you perchance may be able to grant it to others." Additional light is thrown on this subject by the vigorous attack which the same Tertullian made after he had become a Montanist. In the first part of his treatise "De pudicitia", he attacks the pope for his alleged laxity in admitting adulterers to penance and pardon, and flouts the peremptory edict of the "pontifex maximus episcopus episcoporum". At the close he complains that the same power of remission is now allowed also to the martyrs, and urges that it should be enough for them to purge their own sins - sufficiat martyri propria delicta purgasse". And, again, "How can the oil of thy little lamp suffice both for thee and me?" (c. xxii). It is sufficient to note that many of his arguments would apply with as much and as little force to the indulgences of later ages.

During St. Cyprian's time (d. 258), the heretic Novatian claimed that none of the lapsi should be readmitted to the Church; others, like Felicissimus, held that such sinners should be received without any penance. Between these extremes, St. Cyprian holds the middle course, insisting that such penitents should be reconciled on the fulfillment of the proper conditions. On the one hand, he condemns the abuses connected with the libellus, in particular the custom of having it made out in blank by the martyrs and filled in by any one who needed it. "To this you should diligently attend", he writes to the martyrs (Epistle 15), "that you designate by name those to whom you wish peace to be given." On the other hand, he recognizes the value of these memorials: "Those who have received a libellus from the martyrs and with their help can, before the Lord, get relief in their sins, let such, if they be ill and in danger, after confession and the imposition of your hands, depart unto the Lord with the peace promised them by the martyrs" (Epistle 13). St. Cyprian, therefore, believed that the merits of the martyrs could be applied to less worthy Christians by way of vicarious satisfaction, and that such satisfaction was acceptable in the eyes of God as well as of the Church.

After the persecutions had ceased, the penitential discipline remained in force, but greater leniency was shown in applying it. St. Cyprian himself was reproached for mitigating the "Evangelical severity" on which he at first insisted; to this he replied (Epistle 52) that such strictness was needful during the time of persecution not only to stimulate the faithful in the performance of penance, but also to quicken them for the glory of martyrdom; when, on the contrary, peace was secured to the Church, relaxation was necessary in order to prevent sinners from falling into despair and leading the life of pagans. In 380 St. Gregory of Nyssa (Ep. ad Letojum) declares that the penance should be shortened in the case of those who showed sincerity and zeal in performing it - "ut spatium canonibus praestitum posset contrahere (can. xviii; cf. can. ix, vi, viii, xi, xiii, xix). In the same spirit, St. Basil (379), after prescribing more lenient treatment for various crimes, lays down the general principle that in all such cases it is not merely the duration of the penance that must be considered, but the way in which it is performed (Ep. ad Amphilochium, c. lxxxiv). Similar leniency is shown by various Councils--Ancyra (314), Laodicea (320), Nicaea (325), Arles (330). It became quite common during this period to favor those who were ill, and especially those who were in danger of death (see Amort, "Historia", 28 sq.). The ancient penitentials of Ireland and England, though exacting in regard to discipline, provide for relaxation in certain cases. St. Cummian, e.g., in his Penitential (seventh century), treating (cap. v) of the sin of robbery, prescribed that he who has often committed theft shall do penance for seven years or for such time as the priest may judge fit, must always be reconciled with him whom he has wronged, and make restitution proportioned to the injury, and thereby his penance shall be considerably shortened (multum breviabit poenitentiam ejus). But should he be unwilling or unable (to comply with these conditions), he must do penance for the whole time prescribed and in all its details. (Cf. Moran, "Essays on the Early Irish Church", Dublin, 1864, p. 259.)

The term Christian writings is often used when speaking of those writings about Christianity, most commonly the early church fathers which are listed below with their writings from the web page in the Related Links below.

The only writings that can be counted on as wholly true are in the bible itself, all others are merely man's attempt to understand, add to, or comment on that holy writing.

Alexander of Alexandria [SAINT]

- Epistles on the Arian Heresy and the Deposition of Arius Alexander of Lycopolis

- Of the Manicheans

Ambrose (340-397) [SAINT] [DOCTOR]

- On the Christian Faith (De fide)

- On the Holy Spirit

- On the Mysteries

- On Repentance

- On the Duties of the Clergy

- Concerning Virgins

- Concerning Widows

- On the Death of Satyrus

- Memorial of Symmachus

- Sermon against Auxentius

- Letters

Aphrahat/Aphraates (c. 280-367)

- Demonstrations Archelaus

- Acts of the Disputation with the Heresiarch Manes

Aristides the Philosopher

- The Apology

Arnobius

- Against the Heathen

Athanasius [SAINT] [DOCTOR]

- Against the Heathen

- On the Incarnation of the Word

- Deposition of Arius

- On Luke 10:22 (Matthew 11:27)

- Circular Letter

- Apologia Contra Arianos

- De Decretis

- De Sententia Dionysii

- Vita S. Antoni (Life of St. Anthony)

- Ad Episcopus Aegypti et Libyae

- Apologia ad Constantium

- Apologia de Fuga

- Historia Arianorum

- Four Discourses Against the Arians

- De Synodis

- Tomus ad Antiochenos

- Ad Afros Epistola Synodica

- Historia Acephala

- Letters

Athenagoras

- A Plea for the Christians

- The Resurrection of the Dead

Augustine of Hippo [SAINT] [DOCTOR]

- Confessions

- Letters

- City of God

- Christian Doctrine

- On the Holy Trinity

- The Enchiridion

- On the Catechising of the Uninstructed

- On Faith and the Creed

- Concerning Faith of Things Not Seen

- On the Profit of Believing

- On the Creed: A Sermon to Catechumens

- On Continence

- On the Good of Marriage

- On Holy Virginity

- On the Good of Widowhood

- On Lying

- To Consentius: Against Lying

- On the Work of Monks

- On Patience

- On Care to be Had For the Dead

- On the Morals of the Catholic Church

- On the Morals of the Manichaeans

- On Two Souls, Against the Manichaeans

- Acts or Disputation Against Fortunatus the Manichaean

- Against the Epistle of Manichaeus Called Fundamental

- Reply to Faustus the Manichaean

- Concerning the Nature of Good, Against the Manichaeans

- On Baptism, Against the Donatists

- Answer to Letters of Petilian, Bishop of Cirta

- Merits and Remission of Sin, and Infant Baptism

- On the Spirit and the Letter

- On Nature and Grace

- On Man's Perfection in Righteousness

- On the Proceedings of Pelagius

- On the Grace of Christ, and on Original Sin

- On Marriage and Concupiscence

- On the Soul and its Origin

- Against Two Letters of the Pelagians

- On Grace and Free Will

- On Rebuke and Grace

- On Rebuke and Grace

- The Predestination of the Saints/Gift of Perseverance

- Our Lord's Sermon on the Mount

- The Harmony of the Gospels

- Sermons on Selected Lessons of the New Testament

- Tractates on the Gospel of John

- Homilies on the First Epistle of John

- Soliloquies

- The Enarrations, or Expositions, on the Psalms

Bardesanes (154-222)

- The Book of the Laws of Various Countries

Barnabas [SAINT]

- Epistle of Barnabas

Basil the Great [SAINT] [DOCTOR]

- De Spiritu Sancto

- Nine Homilies of Hexaemeron

- Letters

Caius

- Fragments

Clement of Alexandria [SAINT]

- Who is the Rich Man That Shall Be Saved?

- Exhortation to the Heathen

- The Instructor

- The Stromata, or Miscellanies

- Fragments

Clement of Rome [SAINT]

- First Epistle

- Second Epistle [SPURIOUS]

- Two Epistles Concerning Virginity [SPURIOUS]

- Recognitions [SPURIOUS]

Commodianus

- Writings

Cyprian of Carthage [SAINT]

- The Life and Passion of Cyprian

- The Epistles of Cyprian

- The Treatises of Cyprian

- The Seventh Council of Carthage

Cyril of Jerusalem [SAINT] [DOCTOR]

- Catechetical Lectures

Dionysius of Rome [SAINT]

- Against the Sabellians

Dionysius the Great

- Extant Fragments

- Exegetical Fragments

Ephraim the Syrian (306-373) [SAINT] [DOCTOR]

- Nisibene Hymns

- Miscellaneous Hymns -- On the Nativity of Christ in the Flesh, For the Feast of the Epiphany, and On the Faith ("The Pearl")

- Homilies -- On Our Lord, On Admonition and Repentance, and On the Sinful Woman Eusebius of Caesarea (c. 265-c. 340)

- Church History

- Life of Constantine

- Oration of Constantine "to the Assembly of the Saints"

- Oration in Praise of Constantine

- Letter on the Council of Nicaea

Gennadius of Marseilles

- Illustrious Men (Supplement to Jerome)

Gregory the Great, Pope (c. 540-604) [SAINT] [DOCTOR]

- Pastoral Rule

- Register of Letters

Gregory Nazianzen [SAINT] [DOCTOR]

- Orations

- Letters

Gregory of Nyssa [SAINT]

- Against Eunomius

- Answer to Eunomius' Second Book

- On the Holy Spirit (Against the Followers of Macedonius)

- On the Holy Trinity, and of the Godhead of the Holy Spirit (To Eustathius)

- On "Not Three Gods" (To Ablabius)

- On the Faith (To Simplicius)

- On Virginity

- On Infants' Early Deaths

- On Pilgrimages

- On the Making of Man

- On the Soul and the Resurrection

- The Great Catechism

- Funeral Oration on Meletius

- On the Baptism of Christ (Sermon for the Day of Lights)

- Letters

Gregory Thaumaturgus [SAINT]

- A Declaration of Faith

- A Metaphrase of the Book of Ecclesiastes

- Canonical Epistle

- The Oration and Panegyric Addressed to Origen

- A Sectional Confession of Faith

- On the Trinity

- Twelve Topics on the Faith

- On the Subject of the Soul

- On All the Saints

- On Matthew 6:22-23

Hermas

- The Pastor (or "The Shepherd")

Hilary of Poitiers [SAINT] [DOCTOR]

- On the Councils, or the Faith of the Easterns

- On the Trinity

- Homilies on the Psalms

Hippolytus [SAINT]

- The Refutation of All Heresies

- The Extant Works and Fragments of Hippolytus: Exegetical

- Expository Treatise Against the Jews

- Against Plato, On the Cause of the Universe

- Against the Heresy of Noetus

- Discourse on the Holy Theophany

- The Antichrist

- Appendix

Ignatius of Antioch [SAINT]

- Epistle to the Ephesians

- Epistle to the Magnesians

- Epistle to the Trallians

- Epistle to the Romans

- Epistle to the Philadelphians

- Epistle to the Smyraeans

- Epistle to Polycarp

- The Martyrdom of Ignatius

- The Spurious Epistles

Irenaeus of Lyons [SAINT]

- Adversus haereses

- Fragments from the Lost Writings of Irenaeus

Jerome [SAINT] [DOCTOR]

- Letters

- The Perpetual Virginity of Blessed Mary

- To Pammachius Against John of Jerusalem

- The Dialogue Against the Luciferians

- The Life of Malchus, the Captive Monk

- The Life of S. Hilarion

- The Life of Paulus the First Hermit

- Against Jovinianus

- Against Vigilantius

- Against the Pelagians

- Prefaces

- De Viris Illustribus (Illustrious Men)

- Apology for himself against the Books of Rufinus

John of Damascus [SAINT] [DOCTOR]

- Exposition of the Faith

John Cassian (c. 360-c. 435)

- Institutes

- Conferences

- On the Incarnation of the Lord (Against Nestorius)

John Chrysostom [SAINT] [DOCTOR]

- Homilies on the Gospel of St. Matthew

- Homilies on Acts

- Homilies on Romans

- Homilies on First Corinthians

- Homilies on Second Corinthians

- Homilies on Ephesians

- Homilies on Philippians

- Homilies on Colossians

- Homilies on First Thessalonians

- Homilies on Second Thessalonians

- Homilies on First Timothy

- Homilies on Second Timothy

- Homilies on Titus

- Homilies on Philemon

- Commentary on Galatians

- Homilies on the Gospel of John

- Homilies on the Epistle to the Hebrews

- Homilies on the Statues

- No One Can Harm the Man Who Does Not Injure Himself

- Two Letters to Theodore After His Fall

- Letter to a Young Widow

- Homily on St. Ignatius

- Homily on St. Babylas

- Homily Concerning "Lowliness of Mind"

- Instructions to Catechumens

- Three Homilies on the Power of Satan

- Homily on the Passage "Father, if it be possible . . ."

- Homily on the Paralytic Lowered Through the Roof

- Homily on the Passage "If your enemy hunger, feed him."

- Homily Against Publishing the Errors of the Brethren

- First Homily on Eutropius

- Second Homily on Eutropius (After His Captivity)

- Four Letters to Olympias

- Letter to Some Priests of Antioch

- Correspondence with Pope Innocent I

- On the Priesthood

Julius Africanus

- Extant Writings

Justin Martyr [SAINT]

- First Apology

- Second Apology

- Dialogue with Trypho

- Hortatory Address to the Greeks

- On the Sole Government of God

- Fragments of the Lost Work on the Resurrection

- Miscellaneous Fragments from Lost Writings

- Martyrdom of Justin, Chariton, and other Roman Martyrs

- Discourse to the Greeks

Lactantius

- The Divine Institutes

- The Epitome of the Divine Institutes

- On the Anger of God

- On the Workmanship of God

- Of the Manner In Which the Persecutors Died

- Fragments of Lactantius

- The Phoenix

- A Poem on the Passion of the Lord

Leo the Great, Pope (c. 395-461) [SAINT] [DOCTOR]

- Sermons

- Letters

Malchion

- Extant Writings

Mar Jacob (452-521)

- Canticle on Edessa

- Homily on Habib the Martyr

- Homily on Guria and Shamuna

Mathetes

- Epistle to Diognetus

Methodius

- The Banquet of the Ten Virgins

- Concerning Free Will

- From the Discourse on the Resurrection

- Fragments

- Oration Concerning Simeon and Anna

- Oration on the Psalms

- Three Fragments from the Homily on the Cross and Passion of Christ

- Some Other Fragments

Minucius Felix

- Octavius

Moses of Chorene (c. 400-c. 490)

- History of Armenia

Novatian

- Treatise Concerning the Trinity

- On the Jewish Meats

Origen

- Origen de Principiis

- Africanus to Origen

- Origen to Africanus

- Origen to Gregory

- Origen Against Celsus

- Letter of Origen to Gregory

- Commentary on the Gospel of John

- Commentary on the Gospel of Matthew

Pamphilus [SAINT]

- Extant Writings

Papias [SAINT]

- Fragments

Peter of Alexandria [SAINT]

- The Genuine Acts of Peter

- The Canonical Epistle

- Fragments

Polycarp [SAINT]

- Epistle to the Philippians

- The Martyrdom of Polycarp

Rufinus

- Apology

- Commentary on the Apostles' Creed

- Prefaces

Socrates Scholasticus (c. 379-c. 450)

- Ecclesiastical History

Sozomen (c. 375-c. 447)

- Ecclesiastical History

Sulpitius Severus (c. 363-c. 420)

- On the Life of St. Martin

- Letters -- Genuine and Dubious

- Dialogues

- Sacred History

Tatian

- Address to the Greeks

- Fragments

- The Diatessaron

Tertullian

- The Apology

- On Idolatry

- De Spectaculis (The Shows)

- De Corona (The Chaplet)

- To Scapula

- Ad Nationes

- (A Fragment)

- An Answer to the Jews

- The Soul's Testimony

- A Treatise on the Soul

- The Prescription Against Heretics

- Against Marcion

- Against Hermogenes

- Against the Valentinians

- On the Flesh of Christ

- On the Resurrection of the Flesh

- Against Praxeas

- Scorpiace

- Appendix (Against All Heresies)

- On Repentance

- On Baptism

- On Prayer

- Ad Martyras

- The Martyrdom of Perpetua and Felicity (Sometimes attributed to Tertullian)

- Of Patience

- On the Pallium

- On the Apparel of Women

- On the Veiling of Virgins

- To His Wife

- On Exhortation to Chastity

- On Monogamy

- On Modesty

- On Fasting

- De Fuga in Persecutione

Theodoret

- Counter-Statements to Cyril's 12 Anathemas against Nestorius

- Ecclesiastical History

- Dialogues ("Eranistes" or "Polymorphus")

- Demonstrations by Syllogism

- Letters

Theodotus

- Excerpts

Theophilus

- Theophilus to Autolycus

Venantius

- Poem on Easter

Victorinus [SAINT]

- On the Creation of the World

- Commentary on the Apocalypse of the Blessed John

Vincent of Lérins (d. c. 450) [SAINT]

- Commonitory for the Antiquity and Universality of the Catholic Faith OTHER WORKS

Liturgies

- The Liturgy of James

- The Liturgy of Mark

- The Liturgy of the Blessed Apostles

Councils

- Carthage under Cyprian (257) [LOCAL]

- Ancyra (314) [LOCAL]

- Neocaesarea (315) [LOCAL]

- Nicaea I (325) [ECUMENICAL]

- Antioch in Encaeniis (341) [LOCAL]

- Gangra (343) [LOCAL]

- Sardica (344) [LOCAL]

- Constantinople I (381) [ECUMENICAL]

- Constantinople (382) [LOCAL]

- Laodicea (390) [LOCAL]

- Constantinople under Nectarius (394) [LOCAL]

- Carthage (419) [LOCAL]

- Ephesus (431) [ECUMENICAL]

- Chalcedon (451) [ECUMENICAL]

- Constantinople II (553) [ECUMENICAL]

- Constantinople III (680) [ECUMENICAL]

- Constantinople/"Trullo"/Quinisext (692) [LOCAL]

- Nicaea II (787) [ECUMENICAL]

Apocrypha

- Apocalypse of Peter (c. 130)

- Protoevangelium of James (c. 150)

- Acts of Paul and Thecla (c. 180)

- Gospel of Peter (c. 190) [DOCETIC]

- The Testaments of the Twelve Patriarchs (c. 192) [EBIONITIC]

- Acts of Peter and Paul (c. 200)

- Gospel of Thomas (c. 200) [GNOSTIC]

- Acts of Thomas (c. 240) [GNOSTIC]

- Acts of Thaddaeus (c. 250)

- Acts of Andrew (c. 260) [GNOSTIC]

- Acts of Xanthippe and Polyxena (c. 270)

- Acts of John [DOCETIC]

- Acts of Philip (c. 350)

- Apocalypse of Paul (c. 380) -- Greek and Latin forms

- Gospel of Nicodemus (Including "Acta Pilati") (c. 150-400)

- The Doctrine of Addai (c. 400) -- This is a Syriac version of the earlier Acts of Thaddaeus (s.v.)

- Assumption of Mary (c. 400)

- History of Joseph the Carpenter (c. 400)

- Gospel of Pseudo-Matthew (c. 400)

- Acts of Barnabas (c. 500)

- Acts of Bartholomew (c. 500) [NESTORIAN]

- Acts and Martyrdom of St. Matthew the Apostle (c. 550) [ABYSSINIAN]

- Arabic Gospel of the Infancy of the Saviour (c. 600)

- Avenging of the Saviour (c. 700)

- Apocalypse of John (unknown date; late)

- Apocalypse of Moses (unknown date) [JUDAISTIC]

- Apocalypse of Esdras (unknown date) [JUDAISTIC]

- Testament of Abraham (unknown date) [JUDAISTIC]

- Narrative of Zosimus (unknown date)

- Gospel of the Nativity of Mary (unknown date; late)

- Narrative of Joseph of Arimathea (unknown date; late)

- Report of Pontius Pilate (unknown date; late) -- First Greek and Second Greek forms

- Letter of Pontius Pilate (unknown date; late)

- Giving Up of Pontius Pilate (unknown date; late)

- Death of Pilate (unknown date; late)

- Apocalypse of the Virgin (unknown date; very late)

- Apocalypse of Sedrach (unknown date; very late)

Miscellaneous

- The Didache (c. 100)

- The Passion of the Scillitan Martyrs (c. 180)

- A Treatise Against the Heretic Novatian (c. 255)

- A Treatise on Re-Baptism (c. 255)

- Remains of the Second and Third Centuries (various dates)

- Apostolic Constitutions (c. 400)

- Apostolic Canons (c. 400) -- See Apostolic Constitutions, Book VIII, Chapter 47

- Acts of Sharbil (unknown date) [SYRIAC]

- The Martyrdom of Barsamya (unknown date) [SYRIAC]

- Extracts from Various Books Concerning Abgar the King and Addaeus the Apostle (unknown date) [SYRIAC]

- The Teaching of the Apostles (unknown date) [SYRIAC]

- The Teaching of Simon Cephas in the City of Rome (unknown date) [SYRIAC]

- Martyrdom of Habib the Deacon (unknown date) [SYRIAC]

- Martyrdom of the Holy Confessors Shamuna, Guria, and Habib (unknown date) [SYRIAC]

- A Letter of Mara, Son of Serapion (unknown date) [SYRIAC]

- Ambrose (unknown date) [SYRIAC]

- Canons of the Thirteen Holy Fathers (various dates)

- The False Decretals (c. 850)