In 1470 Alberti produced designs for the basilica of Sant'Andrea in the centre of Mantua. The site was particularly important to Ludovico Gonzaga (1412-1478), marquis of the city, because it stood close by the Gonzaga palace and contained a relic, the supposed Blood of Christ.
Alberti's design for the façade of Sant'Andrea, like that of the Rimini Temple for Sigismondo Malatesta, draws its inspiration from Roman triumphal arches, but the Mantuan church takes the idea much further, its design at once more monumental and more complex, adapting a classical form rather than seeking to replicate it. The huge central arch of the exterior portico, with its coffered barrel vault, prefigures the height and vault of the nave. It is flanked by proportionately smaller openings, which also correspond to the church's internal structure, and by a giant order of paired Corinthian pilasters. Their smooth surface complements the richly coffered surfaces of the arch, while their height helps to unify the different levels of the composition. A boldly framed triangular pediment crowns the façade.Inside the church Alberti provides excellent visibility of the high altar and its sacred relic, creating a broad, single-aisled space covered with a 18 m wide coffered barrel vault, notably the largest since classical times. To support it, he followed Roman precedent, using not columns but huge piers, between which he placed side chapels.Alberti's careful coordination of elements throughout the entire structure, interior and exterior alike, gave Ludovico Gonzaga the distinction of being patron of the first truly monumental, classicising structure of the fifteenth century.Of all Alberti's buildings, perhaps Sant'Andrea is the one that best fulfills the following statement by Alberti on the desirable balance between decoration and structure: