Santa Maria del Regno church, together with the annexed castle of which ruins remain today, was built in the 11th century by Giorgia, daughter of the Giudice of Torres, as a Palace Chapel. The church is mentioned in the Libellus Judicum Turritanorum of the 13th century.
The church was built in dark basalt stone by Pisan workers (the island in the Middle Ages was under strong influence from the maritime Republic of Pisa). The façade is divided into five sectors and has a salient-shaped façade. In the middle is the portal, surmounted by a double mullioned window. The whole exterior of the edifice is characterized by false columns (lesenes) and Lombard bands; on the right are the remains of the square bell tower, which is missing the upper part.
The interior, on a rectangular plan, has a nave and two aisles divided by columns whose capitals have flower motifs. The nave has a wooden trusses ceiling, while the aisles are groin vaulted. In the semi-circular apse is the large retablo, the largest 16th-century polyptych in Sardinia, located behind the high altar. The table portrays several prophets and saints, as well as episodes in the life of the Virgin Mary. In the middle, within a niche, is the wooden statue of Nostra Signora del Regno, a 'Madonna with Child' wearing royal symbols. The polyptych is dated 1515.
The church's columns have 17th-century paintings with Apostles and other Saints, while also present is a lesser retablo from the same school, a carved wooden pulpit and an epigraph celebrating the consecration of the church on May 7, 1107.
The Church of St Eustace was built between 1532-1632. St Eustace"s is considered a masterpiece of late Gothic architecture. The church’s reputation was strong enough of the time for it to be chosen as the location for a young Louis XIV to receive communion. Mozart also chose the sanctuary as the location for his mother’s funeral. Among those baptised here as children were Richelieu, Jeanne-Antoinette Poisson, future Madame de Pompadour and Molière, who was also married here in the 17th century. The last rites for Anne of Austria, Turenne and Mirabeau were pronounced within its walls. Marie de Gournay is buried there.
The origins of Saint Eustache date back to 13th century. The church became a parish church in 1223, thanks to a man named Jean Alais who achieved this by taxing the baskets of fish sold nearby, as granted by King Philip Augustus. To thank such divine generosity, Alais constructed a chapel dedicated to Sainte-Agnès, a Roman martyr. The construction of the current church began in 1532, the work not being finally completed until 1637. The name of the church refers to Saint Eustace, a Roman general of the second century AD who was burned, along with his family, for converting to Christianity, and it is believed that it was the transfer of a relic of Saint Eustache from the Abbey to Saint-Denis to the Church of Saint Eustache which resulted in its naming. Jeanne Baptiste d"Albert de Luynes was baptised here.
According to tourist literature on-site, during the French Revolution the church, like most churches in Paris, was desecrated, looted, and used for a time as a barn. The church was restored after the Revolution had run its course and remains in use today. Several impressive paintings by Rubens remain in the church today. Each summer, organ concerts commemorate the premieres of Berlioz’s Te Deum and Liszt’s Christus here in 1886.
The church is an example of a Gothic structure clothed in Renaissance detail. The church is relatively short in length at 105m, but its interior is 33.45m high to the vaulting. At the main façade, the left tower has been completed in Renaissance style, while the right tower remains a stump. The front and rear aspects provide a remarkable contrast between the comparatively sober classical front and the exuberant rear, which integrates Gothic forms and organization with Classical details. The L"écoute sculpture by Henri de Miller appears outside the church, to the south. A Keith Haring sculpture stands in a chapel of the church.
The Chapel of the Virgin was built in 1640 and restored from 1801 to 1804. It was inaugurated by Pius VII on the 22nd of December, 1804 when he came to Paris for the coronation of Napoleon. The apse chapel, with a ribbed cul-de-four vault, has at its centre a sculpture of the Virgin and Child of Jean-Baptiste Pigalle that the painter Thomas Couture highlighted by three large paintings.
With 8,000 pipes, the organ is reputed to be the largest pipe organ in France, surpassing the organs of Saint Sulpice and Notre Dame de Paris. The organ originally constructed by P.-A. Ducroquet was powerful enough for the premiere of Hector Berlioz" titanic Te Deum to be performed at St-Eustache in 1855.