The Monastery of St. Simeon (Deir Amba Samaan) with it towers and walls looms like a Byzantine fortress on a ridge at the head of a desert valley once cultivated with fields and gardens down to the Nile. Built in the 7th century and rebuilt in the 10th, it is the finest example of an original Christian monastery in Egypt, and is highly evocative. Little is known of St. Simeon – he was not the Stylite – and in any case the monastery was first dedicated to Anba Hadra, a bishop of Aswan and saint of the late 4th century, who the day after his marriage encountered a funeral procession and decided to give up the world for a desert cave.

The saint's tomb may have been here, a pilgrims' rest and monastery growing up afterwards. Fearful that the monastery might serve as a refuge for Christian Nubians during their forays into southern Egypt, Saladin destroyed it in 1173. St Simeon was built on a grand scale, with dressed stone walls 10m high.

A small city lay within the walls, with cells for 300 resident monks and dormitories for several hundred pilgrims, as well as bakeries and workshops to support the community. The hills desert around offered solitude and godly communion for probably thousands of monks and hermits.

The lower storeys of the monastery are stone; the upper are mud brick and it is these that have most often into decay or vanished altogether. You enter the portal, and before you, on a height, is the tree-storey keep, open to the sky, cells on either side of the long corridors. Stucco seems to have been applied throughout the monastery, and on it, in the apses of the basilica to your left, are badly damaged paintings. There is a Christ Pantocrator in the central apse; on the sides, the faces of saints have been cut out. Names are carved right into the paintings by Arabs and tourists alike – it is not only time that has taken its toll. The monastery has never been systematically excavated, and repairs have been slight; it is largely a confusion of vaults, staircases, walls, workshops and quarter.

From the tops of the walls there is a glimpse of Aswan, of green, but around 350 of the other degrees there is only the desert sea, luridly red at sundown. Yet there is an evening breeze, and amid the gardens and within the shadow of the towering walls it must have been cool, it is strange to wander round these arches, vaults and apses of familiar shape and significance; and even before the Arabs came it must have been like that, this comforting bastion against the fierce landscape.