Most likely the Columna Lactaria (meaning the Milk Column), where unwanted children were left, was located in front of the Temple of Juno. Anybody who had the desire could have taken them. This habit was practiced all the way until the VI century, when Emperor Justinian established severe punishments for mothers who would abandon their offspring in such a way, which de facto did nothing to decrease the number of unwanted children, but changed the form of setting oneself free of them to a more brutal one. From that time on such children were simply cast into the Tiber. However, before that happened, at the end of the IV century the temple was shut down, thanks to a decree of Emperor Theodosius the Great, forbidding the practice of pagan cults. For centuries the temple complex deteriorated. Probably the buildings were annexed for the needs of Christianity around the VII or VIII century, while one of the temples was converted into a prison (from whence comes part of the church dedication “in carcere” which in Italian means “in prison”). In the XI century the buildings which were close to being a ruin were renovated and integrated, so that a single space was created. The central Temple of Juno was turned into the main nave, while the narrow alleys separating the buildings into side naves. These in turn were supported on the colonnades of the two remaining, surrounded by walls at that time temples of – Spes and Janus. The remaining side temples were torn down – they were used as building material. Along with its modernization the church was given its present-day dedication. Its patron became St. Nicholas of Myra, whose life is drowned in a fog of legends, nevertheless he is known by everyone – he like no other saint has survived in the folk imagination and even today enjoys great popularity – in many countries he comes to good children on the 6th of December and gives out presents, yet surprisingly enough he does not do so in Italy. His cult, widespread in the Eastern Roman Empire, did not reach Italy until the IX century along with the translation of the relics of Nicholas to Bari. Another translation of some of the remains, this time to Rome itself, took place in 1087, which was a direct cause of dedication the church to this saint. It cannot be discounted that the idea came from the Greek-speaking populace of the Eternal City, which lived in this area and which had strong ties to this particular saint.

The next chapter in the life of the church was written at the very end of the XVI century, when its interior was modernized, while the design of a new façade with an elaborate and elegant form was created by Giacomo della Porta. The initiator of these changes was Cardinal Pietro Aldobrandini (the nephew of Pope Clement VIII, from the Aldobrandini family), whose heraldic stars are visible on the elevation as well as inside the church. His surname was also placed on the building façade, which is additionally adorned by two reliefs – one depicts St. Nicholas, the other two saints – most likely Mark and Marcellian.

With the passage of time, many buildings directly adjacent to the church started to spring up, thanks to which for centuries it hid its ancient roots. In the Middle Ages the broad church catacombs served as a burial site, while starting in the XIX century they were used as a place where exorcisms were performed.

It was not until 1932, during the times of Benito Mussolini, when the medieval tissue of the city, around the Theatre of Marcellus, was being removed, and a new communications artery was being set out (present-day via del Teatro di Marcello), that the ancient structure was freed from the latter additions. Particular attention was paid to the central part of the façade, thus uncovering the ancient columns on the sides. In order to strengthen the structure of the building, a medieval bell tower, or more appropriately simply a tower which had been taken apart much earlier was rebuilt.

Descending into the church underground, it is possible to see exceptionally preserved pedestals of the three aforementioned temples and the streets dividing them. They are from the III and II centuries B.C. The remains of the Temple of Juno along with chambers along its side, whose purpose remains a mystery, are the best preserved. Some believe that these rooms were a prisons, others that they contained offices and trading offices as well as rooms of the guards of Forum Holitorium.

The late-Renaissance interior of the present-day church is elegant, however not particularly rich in significant works of art. A fragment of Renaissance fresco, depicting the Madonna with Child merits our attention. Another work from the same time period is a painting in the side chapel (on the left side of the enterance), showing the Resurrection of Christ (1503), attributed to the workshop of Lorenzo Costa. On the other hand the Aldobrandini Chapel contains frescoes of the Baroque painter Giovanni Baglione, who is remembered in history mainly for the fact of being the biographer of Caravaggio, and who hated him with a passion. The reason was the sarcastic and frank way in which the great painter spoke about the lack of talent of his fellow artist.

Paintings in the apse, the wooden ceiling with the heraldic symbols of Pope Pius IX, as well as most of the painting decorations of the interior are from the XIX century, when the church was once again renovated. Looking at the remaining paintings, we should not be fooled: the Baroque canvases adorning this sacral interior are copies of well-known originals.