The arid nature of the Maltese archipelago always made farming difficult. In medieval Malta dry-farming was predominant and the success of the cultivated crop was entirely dependent on the annual rainfall and the adoption of contour ploughing. Peasants suffered widespread financial hardship when rains failed, as was the case for three consecutive years in the late 1460s. But where geology permitted, they employed ground water extraction through the use of subterranean perched aquifer galleries. This is proved by the survival in the Maltese language of the words saqwi (ref. to irrigated lands) and bagħli (ref. to non-irrogated lands). Ġnien (e.g. Ġnien Bazili), and Għajn (e.g. Għajn Tejtes) toponyms are common references to areas containing one or more water springs, within which horticulture and viticulture were commonly practiced. In English language ġnien could be translated as a garden geared towards horticultural cultivation.
In cases of irrigated crops (saqwi) water commonly originated from the underground galleries hewn into Mtarfa Member deposits at right angles to the rock-face, located in the upper terraced sections of the valley. Galleries are generally easily identifiable from their rectangular-shaped rock-cut entrance (or exit) that is on average 0.8m wide and a bit more than 1.5m high. There are several instances, however, where the gallery’s opening lies inside a cave, such as the Għar ta’ Baldu and il-Qattara, two manmade artificial springs in Wied ir-Rum area. The depth of galleries is unknown, but some of the recorded water tunnels may be well over half a kilometre deep. The surveying of perched aquifer galleries is a work in progress and more data in this respect will be present in the coming years. In order to ease the flow of the water retrieved from the perched aquifer, a canal is often carved into the floor of the gallery.
The galleries provide the surrounding area with a perennial supply, though the water volume varies from gallery to gallery. Sure, their supply is subject to yearly rainfall fluctuations, but even so, most of them yield a surprising high volume of water even during the dry summer months. Generally, their exit point is situated at the level of the highest terraced field on a valley side and from there water is transported to the downstream fields through stone canals. Water reservoirs are sometimes located right next to a gallery’s exit. In cases when galleries are located inside a cave they are often fronted by an internal, partly rock-cut, partly masonry built reservoir. Some of the galleries have vertical aeration shafts that pierce the roof of the galleries at intervals.
At Wied ir-Rum alone, over eighteen water galleries have been identified supplying the valley with abundant water to sustain and support an ecological niche which would otherwise not survive. Another fifteen galleries are hewn into Mtarfa Member deposits in the upper cliff-face section at Dingli. A large concentration of identical galleries has been identified at Mtaħleb and elsewhere. Similar galleries as those found in Wied ir-Rum are recorded in other areas of Malta and Gozo possessing similar geological stratifications.
Water galleries are also found in the fortified settlements of the Gozo Citadel and Mdina, the medieval capital of Malta. According to an on-going research their water supply mainly depended on a series of galleries tunnelling beneath the bastions. A series of vertical shafts piercing the galleries’ roofs at intervals allowed the retrieval of water from within the fortified settlements. Such a well is found at Palazzo Falsone — a late-medieval house of distinction in Mdina, which probably accessed a water gallery. By ‘pozzo di aqua viva’ (= a well of running water), Abela writing in 1647 also probably refers to a number of such water sources. In areas where the perched aquifer was unavailable, the only possible modes of water collection were through the collection of surface run-off water and its storage in underground cisterns, and the accidental tapping of the mean-sea level aquifer.
The Maltese galleries are very similar if not identical in hydraulic principle and technology with galleries widely diffused in the Islamic and, before it, in parts of the roman world. Comparison with qanat and cuniculi technologies concludes that the Maltese galleries are very similar in method of construction, location and geology to qanats that have a Persian origin. The study of these water systems is at present the subject of further ongoing research.