High Quality Content by WIKIPEDIA articles! Roman military borders and fortifications were part of a grand strategy of territorial defense in the Roman Empire. By the early 2nd century, the Roman Empire had reached the peak of its territorial expansion and rather than constantly expanding their borders as earlier in the Empire and Republic, the Romans solidified their position by fortifying their strategic position with a series of fortifications and established lines of defense. Historian Adrian Goldsworthy argues that the Romans had reached the natural limits which their military traditions afforded them conquest over and that beyond the borders as fortified in the early to mid Empire lay peoples whose military traditions made them militarily unconquerable by the Romans. In particular, Goldsworthy argues that the cavalry-based warfare of the Parthians, Persians and Huns presented an insurmountable challenge to the expansion of Rome`s infantry-based armies.