Rabat means suburb in old Arabic and this is indeed because Rabat is the town lying outside the citadel of Mdina. The two towns used to be a single one until the Arabs dug a moat across the hill and fortified its tip creating Mdina. Rabat had walls of its own in Roman times but this can only be seen today in parts of the streetpattern. http://wikitravel.org/en/Rabat (Malta)