Wikipedia
In Hellenistic and Roman Arabia and Egypt, a hydreuma (plural hydreumata) was an enclosed (and often fortified) "watering station" ( Classical Latin hydreuma from Ancient Greek ὕδρευμα from ὕδωρ, water ) at wadis in dry regions. A hydreuma was a manned and fortified watering hole or way station along a caravan route, providing a man-made oasis. Juris Zarins, rediscoverer of the city of Ubar in Arabia, described that site in a ' Nova' interview:
"The site that we uncovered at Shisur was a kind of fortress/administration center set up to protect the water supply from raiding Bedouin tribes. Surrounding the site, as far as six miles away, were smaller villages, which served as small-scale encampments for the caravans. An interesting parallel to this are the fortified water holes in the Eastern Desert of Egypt from Roman times. There, they were called hydreumata."In the 1st century CE, Pliny's Natural History described the current Roman sea-route to India, which had recently been established. The Via Hadriana, the route that linked the Nile with the Red Sea, was established by hydreumata. The annual caravan from Alexandria sailed up the Nile to Keft (Pliny's Coptus).
"From Keft the journey is made with camels, stations being placed at intervals for the purpose of watering; the first, a stage of 22 miles, is called Hydreuma; the second is in the mountains, a day's journey on; [103] the third at a second place named Hydreuma, 85 miles from Keft; the next is in the mountains; next we come to Apollo's Hydreuma, 184 miles from Keft; again a station in the mountains ; then we get to New Hydreuma, 230 miles from Keft. There is also another old Hydreuma known by the name of Trogodyticum, where a guard is stationed on outpost duty at a caravanserai accommodating two thousand travellers; it is seven miles from New Hydreuma. Then comes the town of Berenice where there is a harbour on the Red Sea, 257 miles from Keft."The site of the "Hydreuma of Apollo", Apollos Hydreuma, mentioned by Pliny has yielded papyri in modern times. The hydreumata of Abu Qreiya and of Samut have been surveyed but not excavated. Abu Qreiya, one of these watering places, consists today of a concrete well in the wadi, drilled at the beginning of the 20th century; Aby Qreiya has been surveyed but not excavated.
Another route dictated by hydreumata dug into the beds of wadis linked the barren mountain that was the sole source of Roman "imperial porphyry" with the Nile, the Via Porphyritis, the Porphyry Road.
Along the way are seven hydreumata, or fortified wells, each one a day's march from the next. Outside the fortifications are lines of large stones to which oxen were tethered at night." (Werner 1998).