San Carlo alle Quattro Fontane, both in the past and today, has always been identified with the Spanish Trinitarian Fathers and therefore with Spain. It is thanks to the Trinitarian Order and, in particular, to the Spanish religious who lived and continue to live in the convent, that this precious architectural work and the other artistic treasures it houses exist and are preserved.

A fact that links San Carlino to the Kingdom of Spain is the origin of Francesco Borromini. The architect of San Carlo alle Quattro Fontane was born in 1599 in Bissone, a town that today belongs to the Swiss canton of Ticino, but which at that time belonged to the Milanese Empire, when it was under Spanish rule.

Borromini was not only born in Spanish territory and under the authority of King Philip III, but also maintained a strong affective link with Spain throughout his life, dressing and behaving according to Spanish customs. No wonder Pope Urban VIII, clearly pro-French and anti-Spanish, referred to Borromini, with a certain contemptuous tone, as the "spagnoletto".

In the 19th century, the restoration of the Trinitarian Order was carried out from San Carlino by religious, most of whom were originally from Spain. They left a strong Hispanic imprint on the church and convent of San Carlino.

To begin with, in the Spanish coat of arms of the Bourbon Restoration (1874-1931), painted on the ceiling of the Sala de los Venerables (Hall of the Venerables).

At the same time, the present marble floor of the church was donated. The gift was made by Dou00f1a Casilda Iturru00edzar, widow of D. Tomu00e1s Espalza, founder of the Banco de Bilbao; the widow was an illustrious and esteemed benefactor of the underprivileged, as well as a patron of artists.

This fact is attested to by the coat of arms that adorns the floor, which reads: "Mvnificentia piisimae dominae Casildae Itvrrizar vidvae Espalza flaviobrigensis in Hispania pavimentvm hoc stratvm adornatvmqve est. A.D. MDCCCXCVIII" (This pavement was laid and adorned by the munificence of the most pious lady Casilda Iturrizar, widow of Espalza, from Bilbao, in Spain. Year of the Lord 1898).

During the last years of the 19th and first years of the 20th century, San Carlino welcomed a young sculptor from Arechavaleta (Guipu00fazcoa), called Isidoro de Uribesalgo, who came to Rome to learn about the art of the city and to train at the Institute of Fine Arts and at the Academy of San Lucas.

His are the carvings of the founders of the Trinitarian Order, Saint John of Matha and Saint Felix of Valois, which were exhibited for several years in niches in the church and are now in the Sala De Profundis, in the sacristy; the sculpture of Saint John of Matha that presides over the Borrominian library is also by Uribesalgo.

Another element that links San Carlino to Spain and, more specifically, to the Basque Country, is its fronton. Many people find it striking that there is such a sports court in the very centre of Rome.

This small fronton was built in the middle of the 20th century in what was left of the old orchard, once the Italian State expropriated the rest of the site to build the Ufficio Italiano dei Cambi (the Italian Currency Exchange Department) on it.

Today the San Carlino fronton is in need of renovation so that it can be put back into use.

At the end of the 1990s, Juan Maru00eda Montijano, a professor at the University of Malaga, learned first-hand about the great treasures housed in the library of San Carlino and became involved in the conservation of the library.

In 2012, Montijano sponsored the signing of an agreement between the Trinitarian community of San Carlino and the University of Mu00e1laga, in collaboration with other cultural entities, for students of Art History, Fine Arts and Architecture to work on the cataloguing of the bibliographic collection, a task that was completed in 2015.

Among the precious bibliographic riches is a copy of the first illustrated edition of Don Quixote.