The British Museum is unique. Behind its grand neo-classical façade lies one of the greatest storehouses of the world's treasures. It has more visitors than practically any other museum in the world - up to four million a year. It is a world within a world: it has its own publishing house, restaurants, security force, social workers, scientists, cleaners, teachers, engineers, and accountants. At base, however, it is a great collecting institution and the assembling, conservation and study of material is its central function.