The Mangapwani Slave Chamber is a few kilometres further up the coast from the Coral Cave. Although sometimes called the Slave Cave, it is a square-shaped cell that has been cut out of the coralline rock, with a roof on top. It was originally built for storing slaves, and its construction is attributed to one Mohammed bin Nassor Al-Alwi, an important slave trader. Boats from the mainland would unload their human cargo on the nearby beach, and the slaves would be kept here before being taken to Zanzibar Town for resale, or to plantations on the island. It is thought that some time after 1873, when Sultan Barghash signed the Anglo–Zanzibari treaty which officially abolished the slave trade, the cave was used as a place to hide slaves, as an illicit trade continued for many years.