Mainz found a first-century temple to Isis and Cybele under a half-built shopping centre and, instead of moving it, built the mall up over it. You take an escalator down from the shops into a black room where glass walkways run around the foundations and a fibre-optic ceiling stands in for the night sky. The best exhibits are the curse tablets: the ordinary, specific grudges people buried here to be settled by two foreign goddesses.