ALCASSAR DO SAL, a town of Portugal, in Estremadura, which has a castle said to be impregnable. It is indeed very strong both by art and nature, being built on the top of a rock which is exceedingly steep on all sides. Here is a salt-work which produces very fine white salt, from whence the town takes its name. The fields produce large quantities of a sort of rushes, of which they make mats, which are transported out of the kingdom. W. long. 9. 10. N. lat. 38. 18.