The archæology of Rome, Part 8

by John Henry Parker

XVII. Aqua Crabra, and Marrana, A.D. 1124.

This stream was brought into Rome in the bed or foss of the river Almo (Flumen Almonis), mentioned in the Regionary Catalogue as in Regio I., and not otherwise accounted for in this enumeration. The water now comes from the Marrana, which has its source near Marino, and from the Aqua Crabra, which comes from Rocca di Papa, near the lake of Albano, some miles further up the hill; the waters of these two streams are united before a part of them is carried through the tunnel of the Aqua Julia to a point of junction with the bed of one of the many branches of the small river Almo. The Almo itself comes also from the hill of Marino, but from a different part of it, and is divided into many branches when it arrives on the low ground of the Campagna. One of these was made use of for this mill-stream, a canal being carried in banks of clay in straight lines, where the old bed of the river passed through low ground, and had been therefore liable to floods; but this old bed or foss was used, to save expense, where it passed through higher ground in its old winding course.

Originally that part of the branch which passes through Rome was alternately wet and dry, as many of the other branches are, and was liable to floods after heavy rains. The main branch of the Almo turns off to the south near the Torre Fiscale, following nearly the same line as the cross-road from the Via Appia Nova to the Via Appia Antiqua, and passing under this road twice. In this part of its course it is generally dry in dry weather; but when it arrives at the head of the valley of the Caffarella, several other springs that never fail run into this old deep foss. One comes from near the villa of the Quintilii, another is called the fountain of Egeria, a third the Aqua Santa, from its medicinal qualities. There is a bath-house built over that spring. The original springs on the hill of Marino bring little water in dry weather, not more than sufficient to supply ponds near to them for the cattle; but, in wet weather, the water runs off in the old deep winding foss, which also drains all that part of the country.

The sources of the Marrana are about a mile above Marino, and nearly three miles from Albano; they are in a long, narrow, deep valley in the rocks, and the water gushes out in several places at short intervals on both sides of this valley, which continues on under the rock on which the small town of Marino is built. Close under the town is a tall medieval tower, and at the foot of this is a piscina of rude early character, the lower chamber of which is still full of water. A specus cut in the rock as a tunnel is also visible at this point. On the side of the valley opposite to the town are the splendid ancient quarries of peperino, called by Vitruvius lapis Albanus, because Marino was in the district of Alba Longa. The stream flows on in the same deep valley, winding down the hill, and, at the foot of it, the Aqua Crabra, coming from Rocca di Papa, is united with it shortly before it is crossed by the bridge on the road to Grotta Ferrata, ten miles from Rome and near the tunnel through which flows part of the united water, the main body going on straight to the river Anio; the part which is carried through the tunnel turns at a sharp angle to the left, or west, towards Rome. At each end of the tunnel is a loch of early character, partly cut in the rock and partly built of travertine, with the grooves of flood-gates. Over the exit from the tunnel is a piece of old wall faced with Opus Reticulatum, of the same rude early character as that of the Aqua Julia.

After the water emerges from the tunnel, it passes in a deep bed to a bridge over the stream of the Marrana, near the piscinæ, six miles from Rome. At this point the deep foss of the river Almo is close to it. This is dry in dry weather, but has abundance of water in wet weather, and here the foss is dammed across; this appears to have been done originally to effect a junction with the water of the Marrana, which from this point flows in the foss of one of the many branches of the Almo that intersect the Campagna in this part. This mountain-stream is a very uncertain one; sometimes the deep foss is full of water, flowing at the rate of five or six miles an hour, at other times it is dry. Numerous winding streams are collected into one at the head of the valley of the Caffarella, near the church of S. Urbano. Here it passes through swampy ground at a place called Aqua Santa, on the cross-road from the Via Appia Nova to the Via Appia Antiqua; here also several springs fall into the deep bed, one of which is miscalled the fountain of Egeria[193]. In dry weather this branch of the river Almo appears to begin here, and from thence to the mouth of this branch near S. Paul’s, mentioned by S. Gregory as the Almo, the water never fails. All the other branches are deep, dry fosses after dry weather, and the branch that now flows through Rome must originally have been frequently dry, and at other times liable to floods[194].

To remedy this evil, a branch was made from the stream, consisting of the Marrana and Aqua Crabra united, which never fails; and, in those parts where the water passes over low ground liable to be flooded, it is carried in a bank of clay covered with sand, and planted with canes. In such a bank it is carried from near the ford in the natural bed of the river at Roma Vecchia to the Torre Fiscale. Between these two points there is a loch with a flood-gate and a lasher, over which the water falls into one of the deep beds or fosses of the Almo; but this deep bed of a mountain-stream has no other beginning than this same stream, here raised in a bank of clay, into which the water of the Marrana has been turned. In other parts where the ground is high, and consequently the water is below the level of the ground, it follows its ancient, natural, winding course in a deep foss. This is the case both near the original point of junction before reaching the ford at Roma Vecchia, again after passing the Porta Furba, and again under the walls of Rome near the Lateran. From Roma Vecchia, passing by the Torre Fiscale to the Porta Furba, it is carried in a bank of clay many feet above the level of the meadows; but after passing the Porta Furba, it again falls into the old deep foss for about a mile at the foot of the Claudian arcade, winding about sometimes on one side, sometimes on the other, then near to a part of the road to Frascati. For the last half-mile to the Porta S. Giovanni, this road is modern on a large bank of earth across the valley or great foss outside the Wall of Aurelian, and for most part of this line the Marrana is carried in a small bank of clay against the side of the larger bank of the road; but before it reaches Rome it falls again, that is, the earth rises on the terrace under the wall, and the Marrana falls into the old deep bed near the Porta Asinaria, after passing through two mills built on bridges, one on the line of the old Via Asinaria, the other of the old Via Lateranensis.

This small stream enters Rome under the Porta Metronia, which is built on a bridge over it[195]. This bridge has a brick arch of the time of the early Empire, partly concealed by a medieval arch in front of it. Shortly after entering Rome the stream passes at the north end of what is now the nursery-ground of the city, called Orto Botanico, and under a bridge on which another mill is built; by the side of it is the road into that large garden, known to have been that of Crassipes, the son-in-law of Cicero, who mentions in one of his letters a flood of this stream carrying wooden shops from the bank in front of it to the Piscina Publica[196].

This is exactly the direction that the stream takes, as it turns at a sharp angle to the north directly after crossing the Via Appia, and passes close to the Piscina Publica; while the Tiber flows from north to south, and a flood of that river would have carried the shops the other way (if it reached that level at all). There is another mill near the angle on the Via Appia. The stream then passes along a curve at the southern end of the Circus Maximus, (washing the foot of a lime-kiln,) then under the slope of the Aventine and through the gas-works on the site of the Carceres of the Circus, then underground and through another mill in the Via della Marrana near the Bocca della Verità. The eighth and last mill is on the bank of the Tiber, and is built over the mouth of the stream, the back of the building resting on the old tufa wall, called the Pulchrum Littus of the Kings, in which an aperture was left for the Almo when that wall was built. The front of the mill is built on medieval arches standing in the bed of the Tiber.

This alteration of the bed of the Almo may have been made at an early period, of which we have no record, and restored to use in 1124, under Pope Calixtus II., or it may have been entirely made out of the remains of the old aqueducts at that time. We have distinct records of the work done then; but in one of these the expression used is reduxit, that is, he “led again” the water from the old arches. In any case, a great benefit to the city was made at that time, and the account of it fairly belongs to the history of the aqueducts, from which it was made. The following account of it is given by the Cardinal of Arragon, in the time of Pope Calixtus II., A.D. 1124:—