Interesting. "natural resources such as [...] waterfalls"? Is this a typo? Or is it talking about small waterfalls for hydro power? -- Which of those six f

Interesting. "natural resources such as [...] waterfalls"? Is this a typo? Or is it talking about small waterfalls for hydro power? -- Which of those six factors was the roman empire lacking? I feel like they could have had all six, but I don't know much about roman history.