Detail showing Christ casting the money-changers out of the temple

The stories of the childhood and life of Christ take up the entire central register on both walls. The scenes painted on either side of the chancel arch perform a crucial transitional function. The Visitation (on the right, below the Virgin of the Annunciation) directly connects the beginning of the Christ cycle with the preceding cycle, dedicated to the Virgin, while the Hiring of Judas (on the left) marks the end of Christ's public existence in a dramatic fashion, and links this cycle with that of the Passion, which begins with the Last Supper.
In this way a perfect connection is established between the three registers: above, stories concerning Jesus' grandparents and parents; in the middle, his earthly life; below, the Passion and the events following his death, up to Pentecost.
For the frescoes in the middle register, Giotto could draw on many visual models, among them the marble pulpits by Nicola and Giovanni Pisano at Siena and Pisa, the mosaic decorations in the Florence Baptistery, and frescoes and mosaics in Rome. In comparison with all these precedents, Giotto's cycle is more detailed and includes a number of important iconographic innovations. The scenes with the strongest compositional resemblance to reliefs are the first two, the Nativity and the Adoration of the Magi.
To appreciate fully what the scenes of the life of Christ originally looked like, we must remember that all the areas painted 'a secco' rather than in the more resistant 'a fresco' technique have disintegrated. The cloaks of some of
the characters - such as that of the Virgin in the first four scenes - were originally painted with the azurite: in its place a greyish shade is left, impoverishing the chromatic effect of the whole.

Sources
The obvious literary source for the life of Christ is the Gospels, especially that of Matthew. There are, however, a few references to the Protevangelium of James (or rather to its transcription in the Golden Legend), such as the presence of a midwife in the Nativity scene.

Iconography
Giotto includes many allusions to works of art and architecture in this series of scenes. Indeed, their sheer quantity has given rise to the suggestion that he may have had access to a sketchbook containing schematic drawings of famous monuments. The baldacchino in the Cosmati style first seen in the cycle of Joachim and Anna returns in the Presentation of Jesus in the Temple; the background of the Massacre of the Innocents contains the apse of a buttressed Gothic church, possibly inspired by San Francesco at Bologna; and there are statues of horses and lions, surely of Venetian inspiration, over the arcade of the church in which the Expulsion of the Merchants takes place.
The Adoration of the Magi is of great iconographic interest because it includes several innovations and what is probably an image of Halley's Comet.