After the excavation and restoration of the catacombs here at the start of the 20th century, the complex was given into the care of the "Brothers of Mercy of Mary Help of Christians" (Fratelli della Misericordia di Maria Ausiliatrice) in 1926. Their brief was to develop it as a pilgrimage destination.
The Barmherzige Brüder von Maria Hilf are a German lay congregation founded by Bl Peter Friedhofen in 1850. He had been a sanitary worker heavily involved in charitable activity for poor and vulnerable people, at a time when there was limited welfare provision for such. The Brothers initially located at Koblenz, but moved their headquarters to Trier in 1888.
The Brothers have never been a big congregation, but spread to France, Switzerland and Luxembourg as well as within Germany where one of their main interests became the care of mentally ill men. This international status led to their gaining papal approval in 1905.
In 1923, they took over responsibility for the catacombs of Santa Domitilla. Given their charism of nursing care, this was odd but it provided them with a Roman headquarters at a time when all international congregations were encouraged to move their Generalates (headquarters) to Rome.
In 1936, they also took over responsibility for cooking meals at the Vatican for the Swiss Guards. This continued until 1960.
In 1950, the Brothers numbered 343 which is about as numerous as they ever were. They developed outreaches in Brazil and Malaysia, and in the mid Sixties decided to build a large new Generalate at Rome. The architect chosen was Ignazio Breccia Fratadocchi. The complex was finished in 1968, and the chapel consecrated in 1970. The name of Casa Domitilla was given.
The Generalate project was conceived in the brief but intense outburst of overall optimism that followed the Second Vatican Council of the Roman Catholic Church. However, the optimism was overtaken by the reality of decline and the investment proved a mistake. In 1970, the Brothers numbered 273. In 2001, they were down to 101 in 17 convents. In 2010, they numbered 70. This sort of collapse is typical of Catholic religious congregations in the period.
So, in 2009 the Brothers decided to pull out of the administration of the catacombs, and this was given over to the Divine Word Missionaries. Further, the Generalate was moved back to Trier and most of the convent premises converted into a pilgrimage hotel. Initially, a small staff of Brothers was kept on here as a Casa procura so as to maintain a presence at Rome.
However, the collapse in numbers continued. In 2016, the Brothers merged with the "Brothers of Mercy of Montabaur" (Fratelli della Misericordia de Montabaur). This congregation had had a very similar charism, and had suffered a similar collapse. After the merger, the Brothers only numbered 63.
At present (2018), the Casa Domitilla is owned by the Brothers. The Diocese still lists four of them as active in Rome, but the website of the congregation does not now include Rome as one of their localities. What seems to have happened is that the entire convent complex has been leased out as a hotel, the "Kolping Hotel Casa Domitilla".
The chapel is still consecrated (2018).
The main convent buildings are pretty ugly flat-roofed blocks, with reinforced concrete frames and pink brick infill. Their aspect is spoiled by horribly messy accretions on the roofs, for which hopefully the architect (otherwise well regarded) was not immediately responsible.
There are two large rectangular multi-storey blocks, aligned perpendicular to each other and some distance apart. A long , narrow wing connects the two, and the chapel entrance abuts this. The sanctuary end of the chapel faces the street, but this is not close -a garden with mature trees intervenes, and the convent driveway is off the main car park for the catacombs. Hence, there is no easy street view of the edifice.
The eastern main block is four-storey, the western one three-storey and the connecting wing two-storey. However, the first storeys of all are below ground level, and this includes the entrance.
The glass-fronted entrance frontage of the convent is, as mentioned, below ground level and approached by a downward slope of the driveway. It is tucked away below a large flat-roofed glass box. On top of this, in complete contrast, is the chapel itself. This is a blank pink brick cylinder, completely windowless and resembling a section of a brick factory chimney.
The roofing arrangements are interesting. From outside you can see a tall cylindrical stained glass lantern, having an abstract pattern evoking red flames with yellow and grey and containing the text Heri hodie semper ("Yesterday, today, for ever"). It is obvious that this is not on the axis of the cylinder, but is displaced along the major axis towards the sanctuary (that is, towards you viewing from outside). It actually lights the altar inside.
The roof itself is in green metal, and has no parapet. It consists of four concentric circles, centred on the lantern and stepping upwards. There is a thin window strip between each.
The layout is not central, as already noted, but the sanctuary occupies the back of the chapel. It is raised on a single-step platform, the step having a convex curve.
The interior wall is also in blank pink brick, but there must be reinforced concrete support piers hidden away in the brickwork. This is because the roof consists of concrete ring-beams stepping upwards around the lantern, and these are supported by radial step-beams emerging from the top of the wall.
The floor is in cream rectangular tiles, with dark grey grout providing a contrast. Actually each tile seems to be slightly trapezoidal, because they are laid radially and their rows focus on the altar. The colour of the grout emphasises this.
The exterior lantern here continues downwards as a floating vertical hollow cylinder, reaching to just over the altar and having stained glass in the same style as outside. The text it bears is Omnia in ipso constant ("Everything continues in him")
The altar is a rough stone block in the form of an inverted truncated pyramid. It has a vertical groove in its front. The lectern is in the same style, a grooved block on a cylindrical column.
There is a prominent bronze sculptural tabernacle on the wall behind the altar, to the left. It features a polished hemisphere having two concentric frames, on a large stone plaque of a very abstract, vaguely lenticular shape and having a hole below the tabernacle.