To enter the shrine of St George, pilgrims must remove their shoes -- or "shose" as the sign describes them.
Rugs cover the stone floor. The impression is of being inside a mosque, but the black-hooded, elderly figure who retreats through a side door is not an imam but a Coptic nun.
The shoeless reverence is for a set of polished manacles anchored in the masonry. "This chain is believed to have shackled [St George] during his torture," a notice explains. "It is a cause of blessing because it was put on the body of the martyr and on it his blood ran."
Padding softly forwards in his socks, a middle-aged Egyptian, with gold watch and floral tie, seizes the shackles and wraps them around his neck. A miserable, sotto voce wail echoes around the apse as his head bobs up and down in prayer.
The Coptic Church, with its miraculous faith and ancient rituals, is reviving despite the problems of operating in an overwhelmingly Muslim society.
The Egyptian government and the United Nations cultural organisation, Unesco, are restoring churches in old Cairo, discrimination is slackening and the Islamist militants who recently targeted Copts have abandoned their murderous sectarian campaign.
In the "Hanging Church", so called because it was suspended over the walls of a pre-existing Roman fortress, tourism is thriving. On sale in an outer courtyard are watches bearing the face of Coptic Pope Shenouda III, Virgin Mary bedside lights and a game of snakes-and-ladders in which sinners spiral down and the righteous climb through prayer.
A large noticeboard shows the precise route taken through Egypt by the Holy Family when it fled King Herod's persecutions.
"We are getting a new generation coming to us," says Arsanios, a monk with a thick black beard and an embroidered cowl, who is visiting the complex of churches in old Cairo. "Things are far better, the government is helping. There are 75 monks now in our monastery, St Paul's on the Red Sea. We even get converts from Islam; but they can't convert officially."
Copts see themselves as descendants of the pharaohs. Their name derives from the Greek aiguptios, meaning Egyptian; and the round-headed Coptic cross is an adaptation of the ankh, a pharaonic symbol representing life.
The Christians along the banks of the Nile split from their eastern Orthodox brethren in 451AD. A subtle theological division -- over the issue of whether Christ had both a human and a divine nature -- soured into resentment of Constantinople's political imperialism.
When the Arabs invaded Egypt in the seventh century, Copts welcomed them because they ended the demands of Byzantine taxation.
The relationship between Muslim majority and Coptic minority has not always been so easy. In the late 1980s the position of the Copts -- thought by some to constitute as little as 5% of the Egyptian population -- became more perilous.
Several Islamic extremist groups, notably al-Gama'a al-Islamiyya, began targeting Copts, because of their religion, as well as tourists and government officials. But there has been little violence in recent years: the public outcry after the massacre of 58 foreigners in Luxor in 1997 persuaded Islamists to change tactics.
A recent United States State Department report noted with approval an improvement in the Egyptian government's "respect for and protection of religious freedom".
Schools have recently reintroduced lessons on Coptic history and culture. Getting official permits to build a new church, however, is said to be much harder than obtaining them for a new mosque.
In the complex of buildings around the Hanging Church workmen are busy restoring walls under the eyes of the tourist police. A party of saffron-and-red-robed Buddhist monks stand admiring pictures of Coptic popes. "No entry with unsuitable clothing," a sign warns at the entrance.