The city's religious animation after the Council of Trent (1545-1563) was entrusted to the confraternities, groups of laymen consecrated to the main mysteries of Christian life, while at the same time busy with charity work. The confraternity premises needed spaces of worship for the liturgical functions of the confreres who - in a sort of competition in the magnificence of devotion - during the XVII and XVIII centuries took on the shape of actual monumental churches, which go side by side or add to the framework of parishes and religious houses; one just has to think about the role and artistic value of the chapels of the confraternities of the Santo Sudario and Spirito Santo, in the old city centre.
The Confraternity of the Santissima Trinità was founded in 1577 and was first located at San Pietro de Corte Ducis, between the cathedral and town hall; to find new spaces, the confreres succeeded in getting the unsafe St. Agnese church knocked down as well as some adjacent buildings, In the area at the crossroads between the major straight axis of the city (via Dora Grossa, now via Garibaldi) and the street towards the new Renaissance cathedral (the present via XX Settembre). The building, probably meant to strongly mark the spot emerging from a still medieval fabric, is now partly incorporated into the XVIII century buildings which remodeled the heart of the Baroque capital city.
The church is set out on a central plan, equilateral triangle inscribed in one circumference, geometric layout with explicit references to Trinitarian symbolism, a main theme in the spirituality of the Confraternity of the Trinità (and which will be taken up again in the layout of the chapel of the Sindone, just a few decades later.)
The project, which dates back to the beginning of the XVII century, is by the Duke's architect and confraternity member Ascanio Vitozzi (1539-1615), who is buried there: this work came after his works on the sanctuary of Vicoforte, the church of Cappuccini in Turin and the new ducal palace. Despite the church being built for the confraternity's use, the size of the liturgical hall is undoubtedly imposing: the diameter of the central space is roughly 17 metres, while the dome, completed in 1661, rises to 47 metres, making it an emerging feature of urban religious landscape, albeit externally incomplete.
The building has been officiated since 1606, but the liturgical furnishings came about afterwards, following both the demands imposed by changing tastes and by fund flows. For three years (1627-1631) the church was seat of the congregation of Theatine friars, who later went on to receive the ducal chapel of St. Lorenzo.
The high altar (1699-1703) is by Francesco Aprile, on a design by Michelangelo Garove: on the altar 'mensa' we find an imposing Eucharistic tabernacle portraying Christ Resuscitated in its shutter panel; above the tabernacle, in the frame of an imposing architecture of free columns in pink marble crowned by a marble ciborium, we find now a XVII century crucifix.
Beyond the screen of columns was the choir of confreres, badly damaged (as the original part of the altar’s wooden sculpture) by the fire in 1943.
The liturgical furnishings nearest the original setting are the left altar (1635), made from a design by Carlo di Castellamonte as a gift for theconfrere president Silvestro de Montoliveto: it shows the Santa Maria del Popolo painted towards the mid 1500s by the Flemish painter Caracca (Jean Kraeck), court artist of Duke Emanuele Filiberto, who was also member of the confraternity; this picture of Mary accompanied the confreres from 1595, through the various moves, and was restored in 2014.
The right altar (1734) was made as part of the whole redecoration undertaken under the guidance of Filippo Juvarra from 1718, completed over the following decades by his scholar Giovanni Pietro Baroni di Tavigliano. On the Juvarrian altar we see an altarpiece with la Madonna e i santi Agnese, Stefano e Filippo Neri by Ignazio Nepote (Maryand the saints Agnese, Stefano e Filippo Neri), showing the synthesis of dedications of previous churches and the foundation of the Roman confraternita della Trinità, promoted by St. Filippo in 1548.
The facade on via Garibaldi dates to 1830 (design by Angelo Marchini, bas-reliefs by Domenico Banti). The dome, after the 1846 restoration by Giuseppe Leoni, was frescoed by Luigi Vacca and Francesco Gonin following the theme of Gloria della Santissima Trinità in Paradiso (Glory of the Holy Trinity in Paradise). The building received serious bomb damage in July 1943, particularly the destruction of the choir (with the decorations, furnishings and archive), rebuilt after the war.
L'Arciconfraternita della Santissima Trinità, as well as liturgical functions and the common prayer of the confreres, is active with four works of charity according to the tradition of its mandate: maintenance, restoration and enhancement of the church complex, of its choir and sacristy; ' social housing' in apartments near the church; the Fondazione Crocetta, owner of the rest home in the Crocetta neighbourhood since the late XIX century; a Catholic university residence in vicolo Crocetta is being built.
As well as the activities of the Arciconfraternita, the church hosts prayer moments and projects by the Pastorale Universitaria Diocesana.