Mankind has always had an impulse toward mimesis, toward telling a story through action, so long before the Renaissance brought the ideas and “rules” of Dionysian theatre to the western world, laymen had told stories and taught lessons around the campfire or in public areas; the “moralities” of the Middle Ages, the best known today being “Everyman,” were of such impulses; their very nature precluded very much written record.
Another, better preserved “theatre” was the offshoot from liturgical services of the Roman Catholic Church; certain elements of the Christian story lent themselves to enactment, notable among them the birth of Christ. When the events and characters – the shepherds, the angels, the three kings – were fleshed out by deacons and young priests in the pulpit and before the altar, the enactments began to crowd out the actual Mass, and when superiors ordered the actions out of the church, they became playlets on the steps of the church, before or after the Mass itself. These “tropes” – the most famous being the “Quem Quaeritis” (“Whom do you seek?”).
The next step in the development of drama during the Middle Ages were the rise of Corpus Christi plays – a fascinating series of movable stories from the Old and New Testaments, on “pageants” (Wagons), produced and performed by guild members of town, through the streets of Coventry or Lincoln, York, etc. and preserved in manuscripts held by the local priests (thus their preservation). A particularly clever playlet of the birth of Christ was the “Second Shepherd’s Play” which includes a parody of the birth based on the “Lamb of God” reference to Christ in Christian liturgy.
Dramas were banned by the church in the 5th century, along with the fall of Rome. In the 9th century, plays rose up again as "tropes" in the church. At this point, dramas were mainly based around spiritual events from the Bible (Easter, Christmas, etc.). Eventually, three types of plays presented themselves to the general public: Mystery, Miracle, and Morality. Mystery plays were based on scenes from the Bible. Miracle plays did not focus on the Bible, but on the saints and the miracles of their lives. Finally, morality plays were just what they sound to be--plays which teach others how to live a moral life "a story with a moral", so to speak.
By the mid-15th century to the 16th century, morality plays had become the main type of play available to the public--and had risen greatly in popularity. Of course, many of the morality plays which began to develop lost the "lesson" within and became more of the modern play we see today. In fact, Canterbury Tales is a good example of the type of stories and plays that would be seen during this time period.
These morality plays would also often involve allegory. Allegory is when a message or meaning is demonstrated symbolically (I.E. in Pilgrim's Progress, the different struggles (greed, etc.) a man goes through in life actually become real people. Other examples of allegory in middle evil texts would be "the character of Knowledge in Everyman, The Seven Deadly Sins in The Castle of Perseverance, Mercy and Mischief in Mankind" (see source one).
Once plays became more secular, the type of play called the "farce" became much more popular than the religious tropes. Farces were typically humorous plays or comedies where everything went hilariously wrong for the main character. In the secular realm, they also enjoyed seeing gods and great heroes living out their lives and rising from nothing (or being conquered) on the stage.
Texts to examine from Medeival Literature: Gawain and the Green Knight, Canterbury Tales