The Chapel

The work on a fresco cycle in the Cappella Maggiore of the church San Francesco had already begun in 1452 when Piero della Francesca visited the city. The Florentine painter Bicci di Lorenzo was working in the chapel, he died in 1452, leaving the decoration of the chapel barely begun. Piero probably began to work right after Bicci's death, covering in a few years the walls of the Gothic chapel with the most modern and most advanced - in terms of perspective - frescoes that the Italian 15th century could have created.
The 13th century Crucifix with Saint Francis was already in the church when Piero della Francesca frescoed the chapel; it has been recently placed above the main altar.

The Frescoes

The subject-matter of the stories illustrated by Piero is drawn from Jacopo de Voragine's "Golden Legend", a 13th century text that recounts the miraculous story of the wood of Christ's Cross. This popular text, typical of the medieval love for accounts of miraculous events, inspired several other fresco cycles in the 14th and 15th centuries in churches belonging to the Franciscans. The most important iconographical precedent for Piero's stories is Agnolo Gaddi's frescoes painted for the Franciscans of Santa Croce in Florence.
The story tells how Adam, on his deathbed, sends his son Seth to Archangel Michael, who gives him some seedlings from the tree original sin to be placed in his father's mouth at the moment of his death.  The tree that grows on the patriarch's grave is chopped down by King Solomon and its wood, which could not be used for anything else, is thrown across a stream to serve as a bridge. The Queen of Sheba, on her journey to see Solomon and hear his words of wisdom, is about to cross the stream, when by a miracle she learns that the Saviour will be crucified on that wood. She kneels in devout adoration. When Solomon discovers the nature of the divine message received by the Queen of Sheba, he orders that the bridge be removed and the wood, which will cause the end of the kingdom of the Jews, be buried. But the wood is found and, after a second premonitory message, becomes the instrument of the Passion.
Three centuries later, just before the battle of Ponte Milvio against Maxentius, Emperor Constantine is told in a dream, that he must fight in the name of the Cross to overcome his enemy. After Constantine's victory his mother Helena travels to Jerusalem to recover the miraculous wood. No one knows where the relic of the Cross is, except a Jew called Judas. Judas is tortured in a well and confesses that he knows the temple where the three crosses of Calvary are hidden. Helena orders that the temple be destroyed; the three crosses are found and the True Cross is recognized because it causes the miraculous resurrection of a dead youth. In the year 615, the Persian Kin Chosroes steals the wood, setting it up as an object of worship. The Eastern Emperor Heraclius wages war on the Persian King  and, having defeated him, returns to Jerusalem with the Holy Wood. But a divine power prevents the emperor from making his triumphal entry into Jerusalem. So Heraclius, setting aside all pomp and magnificence, enters the city carrying the Cross in a gesture of humility, following Jesus Christ's example.
It should be noted that the order of the execution of scenes is not corresponding to the order of the story. This is probably due to technical reasons, the scaffolding was lowered only after finishing the upper part of the wall. The location on the wall of the scenes and the other frescoes painted by Piero in the chapel but not related to the story of the Golden Legend is also shown on the figure.