Basilica of Sant'Andrea, Mantua

• 1. Introduction

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  Ludovico III Gonzaga commissioned the Basilica of Sant'Andrea in Mantua, Lombardy, and construction began in 1472. The church did not reach completion for another 328 years. Its architect was Leon Battista Alberti, who designed the building on the site of a former Benedictine monastery. That monastery's bell tower, built in 1414, still stands attached to the church today. Later changes and expansions altered pieces of Alberti's original plan across the centuries that followed. Even so, this Roman Catholic co-cathedral and minor basilica, which looms over the Piazza Mantegna, is still counted among Alberti's most complete surviving works. What kept builders returning to this one site for more than three centuries? And what filled the space beneath its dome, drawing pilgrims from across Europe long after Alberti was gone? The answers lie in an architectural experiment modeled on an ancient Roman arch, and in a relic the faithful believed held the blood of Christ himself.

• 2. The Roman Arch Reimagined

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  A single soaring arch dominates the facade, flanked by Corinthian pilasters, styled after the ancient Arch of Trajan at Ancona. Two smaller openings flank that central arch, one on each side. Brick forms most of the structure, its surface finished in hardened stucco. Alberti combined two classical orders at once. A lower order of fluted Corinthian columns pairs with a giant order of taller, unfluted pilasters rising above them, and no one had integrated the two orders quite this way before. A pediment tops the facade, and above it sits a vaulted structure whose exact purpose is unknown. Historians presume it was meant to shade the window opening into the church behind it.

  Alberti repeated the same triumphal arch motif inside the church, matching the facade's design to the interior elevations. Like the exterior, the arcades inside alternate tall arches with much lower, square topped openings. That correspondence between outside and inside stood at the center of Alberti's plan for the whole building. Behind that arcade, the nave was about to be covered by a barrel vault. It was a Roman form that no one had attempted at this scale in over a thousand years.

• 3. Built in Stages

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  A barrel vault stretches the length of the nave, one of the first times since antiquity that architects attempted such a vault on a monumental scale. Alberti probably modeled it on the Basilica of Maxentius in Rome. He may have planned to coffer the vault, the way the shorter barrel vault above the entrance was later built. Money ran short, though, and builders raised a plain barrel vault instead, painting on coffers to imitate the carved look. Alberti's original design also left out a transept, and possibly a dome altogether. Construction of this first phase wound down around 1494.

  In 1597, builders finally added the lateral arms that Alberti's plan had once omitted, and finished the crypt beneath the church. The dome came later still. Architect Filippo Juvarra designed the massive dome that now crowns the church, built between 1732 and 1782. Paolo Pozzo and other artists added the final interior decorations across the late 18th and early 19th centuries. Each addition pulled the finished church further from Alberti's original blueprint. That completed dome would come to shelter a relic already waiting in the crypt below, one that had drawn pilgrims to Mantua for centuries.

• 4. Blood of Christ

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  Every year on the feast of the Ascension, a vial is carried up from the crypt below, through a hole in the floor beneath the dome. The faithful believe it holds the blood of Christ himself. This ceremony was the entire reason the new church was built: to receive the pilgrims who came to witness it. The relic, kept inside vessels described as Sacred Vessels, carries the name Preziosissimo Sangue di Cristo, meaning Most Precious Blood of Christ.

  According to tradition, the Roman centurion Longinus first brought the blood to Mantua. He was said to have scooped up the earth soaked with Christ's blood at the foot of the cross. That legend would not become church-endorsed fact until an emperor named Charlemagne stepped in.

• 5. A Relic's Long Journey

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  In 804, the Holy Roman emperor Charlemagne secured Pope Leo III's authentication of the relic, clearing it for public veneration. Many scholars trace the founding of the Diocese of Mantua back to that papal recognition. They link it too to the construction of the first portion of the Cathedral of St Andrew. The relic disappeared from view for generations before its rediscovery, called the secunda inventio, around 1049. That rediscovery took place in the presence of Matilda of Tuscany. Pope Leo IX confirmed the relic's authenticity again in 1053, and veneration of it grew especially intense during the Renaissance.

  Each Good Friday, the church still displays the relic to the faithful and carries it in procession through Mantua's streets. Charlemagne himself is said to have carried part of the relic away from the city, to St Chapelle in Paris. Other portions later traveled to Weingarten Abbey and to the Archbasilica of St. John Lateran in Rome. Still more went to the Church of the Holy Cross in Guastalla, built on behalf of Beatrix of Canossa. Not every relic inside Sant'Andrea's walls came from Jerusalem, though. Elsewhere in the church, side chapels held tombs and artwork bearing witness to Mantua's own history.

• 6. Chapels and Legacy

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  Alberti abandoned the basilica's usual side aisles and instead lined the nave with chapels branching directly off it. He argued that rows of columns would block worshippers' view of ceremonies happening at the altar.

  One of those chapels belongs to the early Renaissance painter Andrea Mantegna, whose tomb it holds. A bronze figure of Mantegna, made by Gianmarco Cavalli, stands inside, alongside a Holy Family that Mantegna painted himself. Other chapels display frescoes from the school of Giulio Romano, though the version attributed to Giulio himself is now a copy, along with work by Correggio.

  High in the bell tower hang five bells, tuned to A, C sharp, E, F sharp, and A, all cast in the 19th century. Federico I Gonzaga, Marquess of Mantua, is the only burial the church commemorates by name, resting not far from Mantegna's own chapel and its bronze likeness of the painter.