In August 1577 El Greco was formally engaged by Diego de Castilla (1510/15-1584), dean of Toledo Cathedral, to paint three altarpieces for the Cistercian convent of Santo Domingo el Antiguo. The two side altars were to be decorated with The Adoration of the Shepherds (now in private collection) and The Resurrection (still in situ), while the main altar received an enormous, multi-tiered altarpiece with six canvases that had as its focus The Assumption of the Virgin (signed and dated 1577, now in the Art Institute, Chicago) and The Trinity (Prado, Madrid). The complex was among the most ambitious of El Greco's career and constituted one of his finest achievements. The missing canvases - The Assumption of the Virgin, The Trinity, and the half-length figures of Saint Benedict (Prado, Madrid) and Saint Bernard (private collection) - have been replaced by copies, so that the character of the altarpiece can still be appreciated.El Greco's talents doubtless came to the attention of Don Diego through his illegitimate son Luis, whom the artist would have known in Rome in about 1571-75. It is possible that El Greco was approached for the commission in Rome and that his move to Spain was prompted by the prospect of this magnificent opportunity. Certainly, this commission initiated El Greco's career in Toledo in the most auspicious manner conceivable.El Greco was supplied with plans of the church as well as designs for the frames of the lateral altarpieces drawn up by Juan de Herrera, Philip II's architect at the Escorial. El Greco had furnished drawings for the project and he promised to paint the specified scenes to the complete satisfaction of Don Diego and to remain in Toledo until the work was finished. Additionally, he was to superintend the design of the frames as well as of a tabernacle and five statues to adorn the main altarpiece - two of Prophets and three of Virtues (Faith, Charity and Hope). Like the frames, these statues were carved - with significant modifications - by Juan Bautista Monegro (c. 1545-1621), who was also responsible for the cherubs holding an escutcheon with the sudarium.This involvement with the frames of his altarpieces as well as with their sculptural adornment was to become typical of El Greco, who owned the architectural treatises of Vitruvius and Serlio and in Venice had learned to model figures in clay and wax to study elaborate poses. It was by means of his carefully articulated, almost rigorously classical frames that El Greco created a neutral foil for the agitated, spiritual world his paintings conjure up. In the great Assumption of the Virgin, the Apostle closest to the picture frame turns his back to the viewer, thus closing off the steep, notional space of the painting: the viewer is a distanced spectator. By contrast, in the smaller, lateral altarpiece of The Adoration of the Shepherds, a half-length figure of Saint Jerome seems to pose a book on the edge of the frame and turns to address the viewer, serving as a link between two worlds: he is painted in a distinctly more realistic style than the figures of The Adoration, positioned deeper in space, and he thus serves as a mediator between the real and the fictive.