Frere Treaty was an treaty signed between Britain and the Sultanate of Zanzibar in 1873. Signed by Barghash bin Said of Zanzibar, it formally prohibited all import of slaves to the Sultanate of Zanzibar and forced the closure of the slave market in Zanzibar Stone Town. It made it possible for the British to stop all slave ships in the Indian Ocean, becoming a major blow to the Indian Ocean slave trade.