Charterhouse Square is a historic square in Smithfield, central London. It lies between Charterhouse Street and Clerkenwell Road, in the extreme south of the London Borough of Islington, just north of the City of London. In 1371 a Carthusian monastery was founded by Walter de Manny on what is now the north side of the square. It was established near a 1348 plague pit, which formed the largest mass grave in London during the Black Death, and tens of thousands of bodies were buried there. The name of the monastery, Charterhouse, was derived as an Anglicisation of La Grande Chartreuse, whose order founded the monastery.