Occasionally artists are also theologians, giving visual form to ideas about God. Such was Raphael, called to fresco Pope Julius II’s apartments in the Vatican in the years that saw Michelangelo at work on the Sistine Chapel ceiling and Bramante on the new St Peter’s.

Raphael’s theological gift is clear in the pope’s private library – the room later called Stanza della segnatura – in a mural which illustrates the truths of Catholic thought in a way at once simple and compelling. Called the Disputa del sacramento (“Dispute on the Sacrament”), this work celebrates the shared conceptual heritage of medieval Christendom barely six years before Luther opened the divisive season of the Reformation.

The Disputa was executed between 1509 and 1511; Luther’s 95 Theses were published in 1517. Raphael’s fresco entirely fills the library’s 25ft-wide western wall. The composition is cruciform, with a cloud platform dividing the wall horizontally, intersected by the vertical alignment of God the Father, at the top; Christ his Son, in a circular nimbus below the Father; and, below Christ, in a smaller nimbus, a dove representing the Holy Spirit. Below the Spirit – on an altar placed on steps that rise from the scene’s pavement – a circular gold monstrance with the consecrated host echoes the nimbi of Christ and the Spirit. The Sacrament thus exposed draws the attention of numerous figures around the altar, who represent the Church on earth seeking to understand the Eucharistic mystery, while the personages on the cross’s horizontal element – the cloud platform – represent the Church in heaven.

The Disputa is a visual summa, with the Trinity, the Eucharist, the Church triumphant, the Church militant, and – at right and left of the Spirit – four open books representing the Gospels. Prepared observers, such as those admitted to the pope’s library must have been, would moreover have noted a nuance in Raphael’s depiction of the Trinity, with the Holy Spirit placed below Christ and the Father, as if “proceeding” from them. This was not the customary way of showing the three Persons at that time, when the Spirit was normally positioned between the Father and the Son. Raphael modified the standard scheme, perhaps at the insistence of the pope’s theologians, who must have reminded him that 70 years earlier, during the Council of Florence (1439), the Latin Church had reaffirmed its belief, different from that of Eastern Christians, that the Holy Spirit is not only the Spirit of the Father but also of the Son, who together send him to the Church.

The Disputa, facing the door then used to enter the library, was the first image Julius’s visitors saw. Once they crossed the threshold, however, visitors would have become aware of Raphael’s other frescoes in the library, and especially of that on the eastern wall, opposite the Disputa, known as The School of Athens; the two images in fact constitute a single scene. On the one hand, noble figures of ancient philosophers in the School emerge from the depths of a vast hall still in construction: at the centre is Plato, whose raised right hand indicates the heavens, while next to him Aristotle gestures towards the earth.

Various attributes identify other of the ancient thinkers as Socrates, Pythagoras, Heraclitus, Diogenes, Euclid, Zoroaster and Ptolemy. Some of these form animated discussion groups, others remain alone, but the whole assembly seems to advance towards the viewer—an impression reinforced by the perspective lines of the grand hall. On the facing wall, then – in the Disputa – Raphael creates the opposite impression, showing the figures at ground level moving away from the viewer, as they turn towards the altar in the liturgical space defined by the hemicycle of clouds. Viewers in the middle of the room thus become part of a collective movement beginning in the School of Athens and ending at the altar of the Disputa.

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