Santa Maria in Posterula is a lost parochial, convent and devotional church that used to stand at the south end of the Ponte Umberto, at the east end of the Lungotevere Tor di Nona in the rione Ponte.
The dedication was to the Blessed Virgin Mary.
This was originally one of the small early mediaeval parish churches which catered for the ordinary population of the built-up area from the Dark Ages, each catering for up to a hundred families or so. Most have been lost, including this one.
The first unambiguous mention is in a bull of Pope Innocent III in 1205. However, in the Liber Pontificalis entry for Pope Nicholas I (858-67), a mention is made of a river flood that entered a postern gate (posterula) named after St Agatha. One scholarly opinion, held by Grimaldi and Armellini, was that this entry referred to the church and that it was dedicated to this saint at the time. This is unprovable.
In the 15th century the name Santa Maria ad Flumen was recorded, and in 16th century the church was also called Santa Maria de Urso, after the street on which it stood.
In 1604, the parish was extended to include that of the nearby church of San Biagio della Tinta (also known as San Biagio Nuovo), which likewise stood near the river. The latter church was abandoned, and a copy of the famous icon of Our Lady of Graces (the original then being venerated at Santa Maria delle Grazie al Foro Romano) was transferred. It reputedly had miraculous powers, and as a result was solemnly crowned at St Peter's in 1653.
In 1662 the church was attached to a little convent founded to be the Roman headquarters of the Celestine congregation of Benedictine monks. The official in charge of it, who liased with the Papal curia, was called the Procurator General. There was a full-sized Celestine monastery within the walls, at Sant'Eusebio all'Esquilino, but back then the Esquiline hill was open countryside and not convenient of access from the city -hence the foundation of this establishment. Unusually, the parochial responsibilities were kept up and the parish was not suppressed as usually happened with such a change of use.
The congregation also had a theological college here for the benefit of its candidates.
The Celestine congregation was destroyed in the French Revolution and its aftermath, and never re-founded. To replace them, the convent and church was granted to the Irish Augustinian friars who had lost their home when the French demolished their church and convent at San Matteo in Merulana. They moved in in 1819, and brought with them their famous icon of Our Lady of Perpetual Succour. This was enshrined here until 1866, when it was transferred to Sant'Alfonso all'Esquilino).
The friars were moved out in 1888, and the complex was demolished to make way for the Tiber embankment. However, some of the frescoes it contained were moved to San Patrizio a Villa Ludovisi where the Augustinian community re-settled there once more in 1892. They took the icon of Our Lady of Graces with them.
The church was in the western part of the Via del'Orso, which used to run as far as the Ponte Sant'Angelo with a range of buildings between it and the river. The line is now taken (more or less) by the Via di Tor di Nona, but the section on which the church stood has vanished beneath the Piazza di Ponte Umberto.
The church was in the south-west corner of the car park now there.
The church was very small, on a simple rectangular plan with a semi-circular apse. Apparently there were two side altars.
Unusually, it was located parallel to the street and had no entrance façade; rather, the street frontage formed by the right hand nave wall was continued by a tiny square porch. Visitors entered this and immediately turned right to enter the church at its bottom right hand corner. It looks as if there used to be a small piazza in front of the church with a passage leading to the water gate, which the monks built over.
As well as the two miraculous icons, the church (in 1839) had an Annunciation attributed to Girolamo Nanni, and a painting (subject not mentioned) by Francesco Pavese. These were noted by Nibby.