ship's centurion is unclear. Squadrons, most likely of ten ships each, were put under a nauarchus, who often appears to have risen from the ranks of the trierarchi.Starr (1960), p. 39 The post of nauarchus archigubernes or nauarchus princeps appeared later in the Imperial period, and functioned either as a commander of several squadrons or as an executive officer under a civilian admiral, equivalent to the legionary primus pilus.Starr (1960), pp. 42–43 All these were professional officers, usually peregrini, who had a status equal to an auxiliary centurion (and were thus increasingly called centuriones [classiarii] after ca. 70 AD). Until the reign of Antoninus Pius, their careers were restricted to the fleet. Only in the 3rd century were these officers equated to the legionary centurions in status and pay, and could henceforth be transferred to a similar position in the legions. Merchant vessels were commanded by the magister navis. If privately owned, the owner was called exercitor navis. The modern term of "master" to designate a captain of a merchant vessel derives from the magister navis. High Command During the Republic, command of a fleet was given to a serving magistrate or promagistrate, usually of consular or praetorian rank. In the Punic Wars for instance, one consul would usually command the fleet, and another the army. In the subsequent wars in the Eastern Mediterranean, praetors would assume the command of the fleet. However, since these men were political appointees, the actual handling of the fleets and of separate squadrons was entrusted to their more experienced legates and subordinates. It was therefore during the Punic Wars that the separate position of praefectus classis ("fleet prefect") first appeared. Initially subordinate to the magistrate in command, after the fleet's reorganization by Augustus, the praefectus classis became a procuratorial position in charge of each of the permanent fleets. These posts were initially filled either from among the equestrian class, or, especially under Claudius, from the Emperor's freedmen, thus securing imperial control over the fleets. From the period of the Flavian emperors, the status of the praefectura was raised, and only equestrians with military experience who had gone through the militia equestri were appointed. Nevertheless, the prefects remained largely political appointees, and despite their military experience, usually in command of army auxiliary units, their knowledge of naval matters was minimal, forcing them to rely on their professional subordinates. The difference in importance of the fleets