At the points where the water enters and leaves the tunnel, considerable pains have been taken to regulate the flow. The channel of stonework at the mouth is placed in a slanting direction so as to break the force of the rush of water. At the end of this first channel is a cross wall with openings, protected by gratings to catch the leaves and floating rubbish. Behind this is a reservoir, similar to the cisterns in use in the Roman aqueducts, allowing the mud to settle before the water entered the tunnel. Next to the tunnel itself there is a closed building to protect the canal from the fall of rocks and stones, and the actual entrance into the rock is faced with a massive portal of wedge-shaped blocks of stone. The water in this enclosure is now used by the fishermen of the lake as a receptacle for keeping fish, and is for this purpose provided with sluices. Hirt thinks that these arrangements at the mouth are very ancient.[140] Others ascribe them to the imperial era. The point where the tunnel emerges from the mountain on the west of Castel Savelli, nearly a mile from Albano, is called Le Mole. The water was there received in a long troughlike reservoir arched over with a stone vaulted roof. From this it ran through five smaller openings into five separate channels, and was so dispersed into the fields for irrigation. At the present time the whole stream is united, and after passing the road to Anzio, thirteen miles from Rome, takes the name of Rio d’Albano, receives the brook from the valley of Apiolæ, and joining the Acqua Acetosa and Cornacciola crosses the Ostian way near Tor di Valle, three miles and a half from Rome, and then discharges itself into the Tiber. It is the opinion of some archæologists that the Romans brought engineers from Greece to superintend the Alban tunnel. This supposition, however, is not necessary. If the Italian engineers could construct the Cloaca Maxima they would be fully equal to the task of tapping the Alban lake.