So the Romans were a resource empire like the Spanish. The coolest book I’ve ever read was 1493 by Charles Mann. He described Potosi, a mountain in Bolivia whose gold financed the spanish empire for 200 years from roughly 1550-1750 at times the silver that flooded into Europe was so vast it helped cause the famous dutch tulip craze. But when the gold ran out, the power of the Spanish vanished.
That has been the great cautionary tale that people have heard since.
What I find interesting is that the tip of the spear and the current economic endpoint of the american space program today is psyche. The amount of precious metals on that asteroid makes the current complete wealth of earth look approximately like a grain of sand.
The technical/engineering difficulty today of getting the precious metals of psyche is about on a level as that of spain getting the silver of petosi in say 1540. ( a bavarian mining engineer figured out how to extract the silver of potosi about roughly 1540.)