Water conduits (lead pipes)

Thomas Staub

The second main distribution box is located in the garden of the peristyle, near the southern portico within a special, stonelined pit (Mau observed its existence but did not clear far enough to find the distribution box. He thought it was another basin and labelled it as a "vasca murata nel suolo", Mau 1876, 145). This box was supplied with water through the largest of the pipes with a diameter of ca. 0.06 m, coming from the distribution box in the kitchen and reaching the box from the west. In the southernmost intercolumnium of the western portico, the place where the tufa stone block was cut through to allow for the insertion of this pipe is easily visible. The connection point is hidden by the western wall of the box’s basin, but it is still clear that there is no tap attached to it (According to Jansen 2002, 51f, the supply pipe never has a tap attached to it). The distribution box itself, as all the pipes, is made of lead, and is 0.23 m high with a maximal diameter of 0.29 m. The seven pipes that deliver the water to the different fountains are attached to that box. To facilitate the description, the pipes will be labelled alphabetically, starting with a in the north and continuing clockwise up to g.
Pipe a, with a diameter of 0.036 m, leads towards the north. It is not equipped with a tap since it ends at the secondary distribution box near the basin; the pipes continuing out of this box could be closed by individual taps. Pipe b has a diameter of around 0.03 m, and is equipped with a bronze tap and provides the fountain in the middle of the peristyle with water. On pipe c a peculiar feature is observable, as also on pipes e, f, g, which are all equipped with a bronze tap: directly after the tap the diameter of the pipe is enlarged (diameter 0.038 m) for around 0.1 m to thereafter be reduced to 0.028 m. This arrangement, for which so far no parallels have been found in the literature on Roman water engineering, must have some functional explanation. One possible interpretation for this is that these features were made to prevent large deviations in the water pressure when closing and opening the taps, the so-called water hammer effect (On the probable existence of the water hammer effect in Roman plumbing, see Hodge 2002, 325).
The function of pipe c that turns southwards after leaving the distribution basin is still unclear: one possibility is that it might have supplied a now lost fountain in the wide easternmost intercolumnium of the southern portico. Cuts into the block of the stylobate could thus indicate where this fountain was installed. The next pipe, d, mentioned by Mau and discussed above, supplied water to the tap at the second column of the eastern portico and therefore did not need a tap at the box. On this pipe with a diameter of around 0.03 m the length of one entire section could be measured between two soldered joints. The resulting distance of 2.92 m corresponds with the 10 feet described by Vitruvius for these elements (The standardisation of the thickness of the pipes is more difficult to establish, since the diameter varies due to the production method and therefore exact measurements are impossible to establish. For this problem , see Mygind 1916, 48-52). Pipe e has a diameter of around 0.05 m (in the enlarged part 0.06 m) and supplied the supposed secondary distribution box in the atrium by the impluvium with water. It is covered by an unbroken cocciopesto floor between the southern stylobate and the southern rear wall of the peristyle after which it reappears in the northwest corner of corridor 10. Through its large bronze tap, the entire decorative water installations in the atrium could be turned off. Conduit f, with a diameter of 0.035 m (enlarged part 0.044 m), provided the water for the two fountains in the southern portico. Finally, pipe g was attached on top of the main distribution box. Once again the destination of the pipe is uncertain, since there are no further water outlets or fountains that would need a connection. If the pipe running eastwards from the northern distribution box in the kitchen did not provide the water outlet in room h with water but instead fulfilled another unknown function, this pipe could have continued towards this outlet. The diameter of its enlarged part is 0.042 m (the other parts are not measurable).