Although the Roman historian Livy (59 BC – 17 AD) lists a series of seven kings of early Rome in his work "Ab urbe condita", from its establishment through its earliest years, the first four kings (Romulus, Numa, Tullus Hostilius and Ancus Marcius) may be apocryphal. A number of points of view have been proposed. Grant and others argue that prior to the establishment of the Etruscan kingdom of Rome under the traditional fifth king, Tarquinius Priscus, Rome would have been led by a religious leader of some sort. Very little is known of Rome's military history from this era, and what history has come down to us is more of a legendary than of factual nature. Traditionally, Romulus fortified the Palatine Hill after founding the city, and shortly thereafter Rome was ""equal to any of the surrounding cities in her prowess in war"".