Nanni di Banco was the son of a stonemason, Antonio di Banco, and probably trained with his father. Both worked primarily for the cathedral and rose to prominence in their guild of the stonemasons and woodcarvers (Maestri di Pietra e di Legname). It is a mark of Nanni di Banco's economic and social standing that, in September of 1418, he was selected for major political office as one of the twelve Buonuomini. High political office was particularly rare for a lower guild member and was an achievement never matched by either Ghiberti or Verrocchio.
Both Antonio and Nanni di Banco were leaders in their own guild, serving several turns as one of the four governing consuls. It is likely that the Four Crowned Martyr Saints, patrons of the guild, were commissioned for their niche on the center west pilaster of Orsanmichele's north facade in 1409, during a period when Antonio di Banco was one of the consuls. Nanni was a busy man, and work on the statues probably progressed slowly. A receipt for slabs of marble for the stonemasons' guild, dating from the fall of 1415, must relate to the Four Crowned Martyr Saints; it suggests that the project was well under way by that date and was probably finished in the next few years, 1416-1417.
The Four Crowned Martyr Saints are carved out of three marble blocks, the two rightmost figures crafted from a single piece. The recent conservation has revealed that the four saints' hair and beards were once completely gilded, while the sandals and the borders of the Roman garments had gilded decoration. During restoration campaigns in the late eighteenth and mid-nineteenth centuries the statues, like most of the marbles of Orsanmichele, were coated with a dark, pigmented oil that probably gave them a bronzelike patina. The effects of pollution accentuated the dark surface of the figures, creating a severe appearance at odds with Nanni's original conception of the sculpture in gleaming white marble and gold.
The rather confusing story of the four crowned martyrs was well known in Renaissance Florence, principally as told in the thirteenth-century Golden Legend by Jacopo da Voragine. It appears that the original four martyrs were beaten to death by order of the emperor Diocletian (r. AD 284-305). Their story became conflated with that of a group of five stonecarvers, also martyred by Diocletian, in this case because they refused to carve an image of a pagan idol. Because of their profession, the five early Christian martyrs were an obvious choice for the guild of stonemasons, but their number seems often to have been understood to be four, as in this case.
Four Crowned Martyr Saints is notable for being the only sculpture at Orsanmichele whose subject represents the guild members as much as their religious patrons. The four saints are easily conflated with the four consuls who served as the guild masters. Beyond their intertwined identities as sculptors and saints, Nanni's four men -- grave but interacting easily with one another -- can be seen as paradigms for the corporate camaraderie at the heart of the guild system. The saints' identification with guild members is reinforced in the lively marble relief at the base of the niche, where they are depicted not as martyrs, but as masons, carvers, and sculptors busy at work -- their professions seemingly more important than their faith.
The sources for the four figures are explicitly Roman: what has been dubbed the "old saint," the figure farthest to the left, echoes portraits of the emperor Marcus Aurelius (r. AD 161-180). Next to him is the figure known as the "young saint," whose portrait is strikingly like the one of Lucius Junius Brutus, cast in the second century BC and now in the Musei Capitolini, Rome. The "middle-aged saint," third from the left, amicably rests his left hand on his companion's shoulder, in direct quotation of a gesture seen on Roman funerary monuments. His right hand is placed next to the right hand of his companion and recalls another gesture seen on similar monuments: the dextrarum iunctio, or joining of the right hands. The somber, earnest gaze of the "middle-aged saint" is also fully in keeping with Roman portraiture. The "speaking saint" anchors the group to the right and, his mouth open, seems to be addressing his companions. It is fitting that Nanni di Banco, or an advisor for him, should have also positioned this figure's right hand and arm in a pose recalling Roman statues of orators.