and triumphal arches, which feature artistic depictions of both fighting men and military machines; the archeology of military burials, battle sites, and camps; and inscriptions, including military diplomas, epitaphs, and dedications. Through his military reforms, which included consolidating or disbanding units of questionable loyalty, Augustus changed and regularized the legion, down to the hobnail pattern on the soles of army boots. A legion was organized into ten cohorts, each of which comprised six centuries, with a century further made up of ten squads (contubernia); the exact size of the Imperial legion, which is most likely to have been determined by logistics, has been estimated to range from 4,800 to 5,280. In 9 AD, Germanic tribes wiped out three full legions in the Battle of the Teutoburg Forest. This disastrous event reduced the number of legions to 25. The total of the legions would later be increased again and for the next 300 years always be a little above or below 30. The army had about 300,000 soldiers in the 1st century, and under 400,000 in the 2nd, "significantly smaller" than the collective armed forces of the territories it conquered. No more than 2% of adult males living in the Empire served in the Imperial army. Augustus also created the Praetorian Guard: nine cohorts, ostensibly to maintain the public peace, which were garrisoned in Italy. Better paid than the legionaries, the Praetorians served only sixteen years. The auxilia were recruited from among the non-citizens. Organized in smaller units of roughly cohort strength, they were paid less than the legionaries, and after 25 years of service were rewarded with Roman citizenship, also extended to their sons. According to Tacitus there were roughly as many auxiliaries as there were legionaries. The auxilia thus amounted to around 125,000 men, implying approximately 250 auxiliary regiments. The Roman cavalry of the earliest Empire were primarily from Celtic, Hispanic or Germanic areas. Several aspects of training and equipment, such as the four-horned saddle, derived from the Celts, as noted by Arrian and indicated by archaeology. The Roman navy (Latin: classis, "fleet") not only aided in the supply and transport of the legions but also helped in the protection of the frontiers along the rivers Rhine and Danube. Another of its duties was the protection of the crucial maritime trade routes against the threat of pirates. It patrolled the whole of the Mediterranean, parts of the North Atlantic