Built in the Baroque style and designed by the Italian Giuseppe Antonio Landi, the small church has an irregular octagonal nave and a central dome.

The Church of Saint John the Baptist was built because the Sé Cathedral was under construction and closed for liturgical acts and there was no safe place to keep the Blessed Sacrament.

[4][5] The current building has a facade based on the classicizing Baroque style, a reference to the academic training of its author, Giuseppe Antonio Landi, who studied at the Accademia di Belle Arti.

The floor plan - conceived as two overlapping squares, the larger being the nave, internally shaped like an irregular octagon, and the smaller being the main chapel, flanked by annexes - is the most distinctive feature of this 19th century project.

Niches, balustrades and windows were carefully composed to accentuate the illusion of depth and non-existent openings, and natural lighting was calculated to emphasize the scenographic effects of this illusionist painting.

On the high and side altars, two frames that would have been used to display paintings on canvas, both depicting the life of Saint John, have been preserved; a lost third panel also followed the same theme.