This is a little long, but gives a little more explanation...
the Chronicles of Narnia
The Chronicles of Narnia is a series of seven fantasy novels for children written by C. S. Lewis. They present the adventures of children who play central roles in the unfolding history of the realm of Narnia, where some animals talk, magic is common, and good is fighting evil. The books are also known for their illustrations by Pauline Baynes. The stories illustrate aspects of Christianity in a way that is accessible to younger children.
Allegory
The Lion, the Witch and the Wardrobe by C. S. Lewis
Although the books contain allusions to Christian ideas, an allegorical reading of these books is quite confusing and extremely reductionist. Lewis, a devout adult convert to Christianity incorporated elements of Christian theological concepts into the stories to make them accessible to children.
In this Lewis succeeds; The Chronicles of Narnia have become favourites with both children and adults. The theology is well incorporated; the books are not weighty in the least, and can be read for their adventure, colour, and mythological ideas without concern for the Christian issues. Lewis himself maintained that the books were not allegorical but "suppositional", more like what we would now call alternative history.
One of Lewis' early academic publications was The Allegory of Love (1936), about medieval allegories of courtly love. Consequently he kept a strict definition of allegory, as he wrote to another young fan:
"I did not say to myself 'Let us represent Jesus as He really is in our world by a Lion in Narnia'; I said, 'Let us suppose that there were a land like Narnia and that the Son of God, as he became a Man in our world, became a Lion there, and then imagine what would happen.'"
In another letter, Lewis clearly states:
"If Aslan represented the immaterial Deity in the same way in which Giant Despair represents despair, he would be an allegorical figure. In reality however he is an invention giving an imaginary answer to the question, What might Christ become like, if there really were a world like Narnia and He chose to be incarnate and die and rise again in that world as He actually has done in ours? This is not allegory at all."
On the other hand, Lewis did have loosely defined parallels in mind, as he wrote to another fan:
"The whole series works out like this:
The Magician's Nephew tells the Creation and how evil entered Narnia,
The Lion, the Witch, and the Wardrobe - the Crucifixion and Resurrection,
The Horse and His Boy - the calling and conversion of the heathen,
Prince Caspian - restoration of the true religion after a corruption,
The Voyage of the Dawn Treader - the spiritual life (especially in Reepicheep),
The Silver Chair - the continuing war against the powers of darkness,
The Last Battle - the coming of Antichrist (the ape). The end of the world and the last judgement."
There are also other parallels with Christian history. Parts of The Magician's Nephew are related to the first three chapters of Genesis, and in The Lion, the Witch, and the Wardrobe, Peter possesses traits similar to those of St. Peter, Edmund is a Judas Iscariot-like figure, and Lucy and Susan reflect Mary Magdalene and the other women when they first discovered Jesus' tomb was empty. Prince Caspian can be said to parallel the Protestant Reformation, with Miraz representing the Papacy, and Caspian, Martin Luther.
Numbering the books, publication order and internal chronology
The books of the series, in the order of their publication, are:
The Lion, the Witch, and the Wardrobe (1950)
Prince Caspian (1951)
The Voyage of the Dawn Treader (1952)
The Silver Chair (1953)
The Horse and His Boy (1954)
The Magician's Nephew (1955)
The Last Battle (1956)
The first American publisher, Macmillan, put numbers on the books and used the publication order. When HarperCollins took over the series, the books were renumbered using the internal chronological order, as suggested by Lewis' stepson, Douglas Gresham.
The Magician's Nephew (1955)
The Lion, the Witch, and the Wardrobe (1950)
The Horse and His Boy (1954)
Prince Caspian (1951)
The Voyage of the Dawn Treader (1952)
The Silver Chair (1953)
The Last Battle (1956)
Gresham quoted Lewis' reply to a letter from an American fan in 1957, who was having an argument with his mother about the order:
"I think I agree with your order (i.e. chronological) for reading the books more than with your mother's. The series was not planned beforehand as she thinks. When I wrote The Lion I did not know I was going to write any more. Then I wrote P. Caspian as a sequel and still didn't think there would be any more, and when I had done The Voyage I felt quite sure it would be the last. But I found as I was wrong. So perhaps it does not matter very much in which order anyone read them. I'm not even sure that all the others were written in the same order in which they were published."
Nevertheless, the reordering has brought ire from many fans of the series, who appreciate the original order which introduces important parts of the Narnia universe in the early part of the series and then provides explanation for them later in the prequels, in particular the creation story in The Magician's Nephew. Other arguments for the publication order include that Prince Caspian is subtitled "The Return to Narnia", and that the following fragments of text from The Lion, the Witch, and the Wardrobe support it as being the first book in the series:
None of the children knew who Aslan was, any more than you do.
That is the very end of the adventure of the wardrobe. But if the Professor was right, it was only the beginning of the adventures of Narnia.