Dating from the sixteenth century but rebuilt in 1867 after Walker’s attack, the historic Convento de San Francisco is two blocks northeast of the cathedral. The attached cultural centre has been converted into Nicaragua’s best pre-Columbian museum, housing various displays and many of the petroglyphs recovered from Isla Zapatera. Hewn from black volcanic basalt in about 1000 AD, these statues depict anthropomorphic creatures – half man, half lizard, turtle or jaguar – which probably had ritual significance for the indigenous peoples who inhabited the islands. It was also from the confines of this convent that in 1535 Frey Bartolomé de Las Casas, apostle of the indigenous peoples of Central America, wrote his historic letter to the Spanish Court, condemning the Indians’ mistreatment at the hands of the Spanish. The Convento also houses the city library; many of Walker’s filibusterers are buried in the catacombs in its basement.