Originally dedicated to Saint Saturn (a martyr from Cagliari), this sacred edifice has got a façade divided into two orders.
The first, th dating from the 13 century, enframes the portal with a lintel sculpted in acanthus spirals, surmounted by a relieving round arch. This latter bears an inscription (bearing the heraldic sign of a priest from Iglesias, Marco Canavera) placed to remember the foundation of a monastery of Clarisses in this church (1620), by will of the same cleric; the convent was th closed down at the end of the 19 century.
The second order shows a Gothic, one-light window and an upper section, with two th windows, dating back to the 17 century; it ends in a broken pediment and a sail-shaped bell tower. One of the bells shows an image of St. Catherine of Alexandria and the date 1649.
The inside has got a single-nave plan, with wooden roof supported by five pointed arches in trachyte, dividing the nave into bays. nd The 2 bay on the left side presents a grate with a small door, used for the Clarisses' Holy Communion.
Incorporated onto the wall of the 5 bay, in a low position, is a burial inscription in memory of the Capuchin priest Benedetto from Iglesias, died in 1713. The slab was transferred here from the church of Valverde, following the institution of Capuchin Friars' community at the church of Madonna delle Grazie. The friars have been officiating this church since 1925.
In the last bay are two small side chapels, dedicated to Saint Francis (on the left) and to the Sacred Heart of Jesus. The intrados of the depressed round arch opening to the presbytery, subdivided in 15 rectangular panels, is decorated by motifs of roses and shells, very similar to those adorning the triumphal arch of the church of San Domenico in Iglesias.
The presbytery area, of squared plan, is surmounted by a dome. This is linked to the underneath space by pendentives and corbels, inserted at the corners; one of them bears an incision of the year 1708.
On the bottom wall, inside a niche, is a wooden simulacrum of Our Lady of Graces, worshipped by the community of Iglesias, as a belief has it that the Virgin would have interceded for the town to be set free from the calamity of locusts in 1735.
All the liturgical pieces of furniture - the altar, the Eucharistic table and the ambo - are recent works made in the attempt to recreate, as far as possible, the presbytery area as it was before modifications of th late 19 century. Therefore, the great wooden reliquary made by Sister Giuseppina Pinna has found a new place onto the new altar. It is a handicraft of neo-Gothic style, in carved, gold-plated wood, guarding the relics of San Placido, donated to the monastery of Iglesias by Pope Gregory XVI in May 1842. Exposed for veneration along the walls of the nave are a few noteworthy canvases of artistic and historical interest, such as a painting of Saint Saturn and another one featuring the Virgin with the Child.
The first (100 x 180 cm) was painted by an unknown author and can be referred to the end of th 16th and the beginning of 17 century.
The second th th (18 -19 century) portrays the Virgin surrounded by Saints Severo and Severino, Cartoforo and Vittorino, worshipped as protectors of masons. This is why the work was probably requested to a local artist by the town Guild of masons, whose seat was hosted right in this church