The task of restoring both the surviving eighteenth-century sacristy and the external structures and decorations of the apse was assigned to the Ravenna office of the Monuments and Fine Arts Service.
A work attributed in the documents to the ducal architect Biagio Rossetti, who first put his hand to it by order of Duke Ercole I, the apse was begun on 19 May and work was completed on 4 August 1499. According to the Cathedral records, the work was almost completely financed by the Cathedral itself and not by Duke Ercole, who was only the promoter, except for the pictorial decoration, regarding the execution of which we find much illuminating information in the contract drawn up by the notary Nicolò Zerbinati, dated 1499.
The document states that the architect agreed to use his own money to pay two good painters (Andrea Costa, from Bologna, and an unknown Modenese) to execute a painting for the choir to be made in accordance with the drawings presented. The judge of the paintings was to be Andrea Mantegna; if Mantegna were to deem the works unacceptable, the paintings were to be removed and the fees paid back to Rossetti.
It would appear, therefore, that Rossetti's apse had pictorial decorations right from its construction, but all trace of these works has been lost. The painting is in fact mentioned nowhere else in the historical record, nor indeed is it mentioned when Bastianino came to work on the Judgement. It may be that - for unknown reasons - the decoration was never made, even though it would have been a singular thing if the city's most important place of worship had been left for almost eighty years without pictorial decorations in the apse, until Bastianino came along.
The apse is one of Rossetti's most representative works and it shows his ductile capacity to renew himself with every project: while a pilaster strip with a corniced border and relative flattened capital had already been used in the church of Santa Maria in Vado, for example, the treatment of the upper surface with a double order of arches, later used again in San Cristoforo, lends the apse a wholly original impact that others lack.
The terra cotta decorations in the southern side of the choir were widely restored in 1950-51, following the repairs made to the area between the nave, apse, and bell tower left empty by the collapse of the "coretto d'inverno". Apart from this situation, and small portions of cornice that had been replaced at various times, the original terra cotta decorations, covered by a thick layer of dust and smog deposits, were under attack by various agents of deterioration.
The state of repair was so poor as to suggest that the external surfaces of the apse - apart from post-war repairs - had never been subjected to general repairs or maintenance. In fact, as soon as cleaning was effected, this first impression was confirmed inasmuch as virtually all of the two cornices and the arches revealed the original white finish. By imitating the colour of natural stone, this finish gave the impression of a structure realized with finer materials.
This same finish, used to demarcate the architectonic elements, was complemented by the masonry beneath, whose coat of russet-coloured plaster gave the impression of brickwork. The apse too, therefore, like other Renaissance buildings in Ferrara by Rossetti and others, used terra cotta and brick, but in order to cover what were only building materials with a coat of plaster whose purpose was at once protective and mimetic. The restoration plan was to conserve this testimony both to Rossetti's architectonic method and the building methods of his day.
Conservative treatment was accompanied by the replacement of elements that were in poor condition or missing altogether, a decision that was as necessary for the interpretation of the decorative structure as it was for its support.