For Jews, there are the remains of the western wall of Jerusalem's Second Temple, also known as the Wailing Wall, the only proof that the temple ever existed. For Muslims, there is the Al-Aqsa Mosque, built on the site from which Muhammad is believed to have ascended to heaven. For Christians, Jerusalem is bound up with the treasured biblical tale of Jesus Christ's last days, his passion and death on the cross, and his subsequent resurrection. The Church of the Holy Sepulchre, Calvary and Via Dolorosa, the Garden of Gethsemane where Jesus prayed the night before he was crucified: these places may touch the heart of even the most hardened of atheists.

But, in Jerusalem, religious exultation can turn into a medical condition, where otherwise normal, healthy people become infected with a sudden madness. Ordinary tourists, who have come on holiday from London, Louisiana, or Lvov, unexpectedly transform into street preachers, laurel-crowned lyre-plucking Romans clad only in hotel bed sheets, or pilgrims hauling heavy wooden crosses who take their 10 minutes of glory extremely seriously. The hospitals in Jerusalem receive on average 20 such cases every week, but the number soars dramatically during major Christian festivals such as Christmas and Easter.

This bizarre condition is known by psychiatrists as the Jerusalem Syndrome and was first identified in the 1930s by Dr Heinz Herman. Those afflicted believe that they are the incarnation of all sorts of biblical characters, with Jesus himself, the Virgin Mary, and Mary Magdalene topping the list hands down. Among the apostles, the most popular characters are Paul, Peter, and Matthew. John the Baptist is also something of a hit.

The symptoms last for about a week, or until the date of the return flight home, whichever comes first. Usually those afflicted by Jerusalem Syndrome remember nothing of the event and go back to their normal lives as dentists, lawyers, businessmen, and so on.  However, the more serious cases require hospitalisation and medical treatment.