Professor Robin Cormack, the curator, said: "It has an inner plain cup with an outer ornate covering. The outer cup can be dated to the sixth century but nobody can say for sure when the inner cup was made. There is still a plausible argument that it is the Holy Grail." He said many exhibits would never be displayed again because they are so fragile. The show begins in AD330 when Roman emperor Constantine changed the name of the city of Byzantium to Constantinople. It became the centre of an empire that held sway over the eastern Mediterranean. The exhibition ends in 1453, when the Turks under Mehmed II captured Constantinople now Istanbul.