This chapter presents the landscape of ancient Trimithis, a polis in the fourth century AD, and a synthesis of its urban layout. The settlement extends over an irregular area in which moving sand dunes determined living spaces and the availability of water. Archaeological evidence attests the presence of a settlement at least from the Old Kingdom below the central hill on which the temple of Thoth stood from the New Kingdom to the Roman period. Our knowledge of the settlement life, history, and layout is still incomplete,but the fourth-century AD phase allows some comparisons with other cities of the Empire. The study of the buildings visible on the surface, of the excavated areas, and of the street layout suggests an imperial regular pattern of streets, with impressive public buildings like the thermae. The layout and architecture of Trimithis as they appear today resemble in several aspects the later Islamic medieval settlements of the oasis: vernacular architecture, compact organization of space, high density of buildings, labyrinthine layout, shaded or semi-shaded streets and alleys, sometimes closed with doors, and a certain disposition to close spaces to avoid exposure to sun and winds.

The comparison of two small oases of the Kharga and Dakhla depressions, in the Western Desert of Egypt, confirmed that spring-fed oases have been attractive after the onset of aridity, ca 4500 BC, but irrigated agriculture has not been proved yet before the Intermediate Period. Irrigated areas were suject to harsh constraints despite the wealth of underground water during millennia: wind-induced dune shifting and soil erosion in Amheida and El-Deir, while flash floods destroyed most of the El-Deir oasis during the Roman period. Recovery was more difficult because artesian springs, which relied on water stored during the wet phase of the Holocene, were progressively exhausted by irrigation practices and could no longer compensate for the drying up of the oasis environment. If natural factors are not the unique causes of economic decay in the oases, they may have some responsibility in the progressive abandonment of agriculture during the third and fourth centuries. Amheida disappeared to the benefit of El-Kasr fortress, while El-Deir retained some importance for caravan trade between Hibis and the Nile Valley thanks to a well secured by a newly built fortress from 288 to the sixth century AD.