The broad flat space to the N.E. of the Quirinal Hill, was occupied by the Thermæ of Diocletian, now converted into the great Church of S. Maria degli Angeli. This enormous group of buildings was the most extensive of all the gigantic edifices of the empire, and the ground plan is not difficult to trace by the aid of the existing ruins. Some idea of their dimensions will be given by remarking that the grand court enclosed a space once occupied by the church, monastery, and spacious garden of the Monks of S. Bernard, the great church and monastery of the Carthusians, two very large piazzas the large granaries of the Papal Government, part of the grounds of the Villa Montalto Negroni, and some vineyards and houses besides. The north-western side of this grand court is now only marked by the remains of two semicircular tribunes in front of the railway station. The rest of the foundations of this side are hidden under the great cloister of the Carthusian monastery, and in the district beyond. The principal entrance was on this side. The south-eastern side is now occupied by the buildings of the railway station, at the back of which were discovered the ruins of a large reservoir now destroyed (K), in the shape of a right-angled triangle. The peculiar form of this building seems to have been necessitated by the course of a public road of some importance confining it on the south side, and it has been supposed, not without reason, that this was the principal road leading out of the city at the Porta Viminalis. The interior was filled with pillars like those which still stand in the ancient reservoirs at Baiæ and Constantinople. [Illustration: The Quirinal Hill, as seen from the Palatine.] On the south-western side of the court there are considerable remains. In the gardens of the monastery of S. Bernardo, part of the cavea of a theatre (A) with a radius of about seventy yards, may be traced, not unlike that in the Thermæ of Titus. The seats of this are gone, but parts of the back wall with niches remain. On each side of this are traces of rectangular chambers, and at the corners stand two round buildings, one of which is nearly perfect, and has been converted into the Church of S. Bernardo. The ancient domed roof with its octagonal panelled work is still standing. Part of the other rotunda at the southern corner is also left, and has been built into the end of the Via Strozzi. [Illustration: THERMÆ DIOCLETIANÆ. (PALLADIO.) _The red lines mark the conjectural restorations._]