To trace the origins of the Roman Empire is to follow the winding Tiber River through the rolling hills and marshes of central Italy, a landscape both fertile and treacherous. The city of Rome itself rose from this patchwork of valleys, seven low hills ringed with dense oak groves and rocky bluffs.

Archaeological evidence reveals early settlements clustering atop these hills by the eighth century BCE, their mud-brick huts and timber palisades a humble beginning for what would become an imperial colossus. Excavations on the Palatine and Capitoline hills have unearthed the postholes and hearths of these first dwellings...