The eunuchs were slaves who did all the work in the Forbidden City, such as cooking, gardening, cleaning, entertaining guests, and the bureaucratic work needed to govern a vast empire. They also served as the emperor's advisers. The eunuchs spoke in a distinctive high-pitched voice, and, to further prove that they were really eunuchs, they had to keep their severed penises and testicles in jars of brine they wore around their necks when working. The Forbidden City was full of treasures that the eunuchs constantly stole and sold on the black market. The business of government and of providing for the emperor created further opportunities for corruption which virtually all the eunuchs engaged in.