Which C.S. Lewis novel begins the Narnia series in its original publication order?

The Lion, the Witch and the Wardrobe begins C.S. Lewis's Narnia series in its original publication order.

Geoffrey Bles published the novel in London on 16 October 1950. It introduces the Pevensie children, the land of Narnia, the White Witch, and Aslan. The story centers on Lucy Pevensie's discovery of a magical country through a wardrobe in the spare room of a country house.

The Magician's Nephew is the chronological beginning of Narnia's internal history, describing the world's creation and the origin of the wardrobe. Lewis nevertheless published it sixth, in 1955. Because modern editions often number the books chronologically, readers may see The Magician's Nephew labeled as volume one; the answer to this question concerns the original publication sequence.