While UV rays can cause skin cancer, because skin cancer usually affects people after they have had children, it likely had little effect on the evolution of skin color because evolution favors changes that improve reproductive success.
The only problem was that I couldn't remember where I had heard that. In fact, I wasn't all that sure that I was right. I know that the Roman Empire lasted rougly 500 years but how about the Egyptians, the Chinese, the Ottomons, etc. I thought that it would be interesting to explore different empires and see how long they lasted. In another article, I talk about the definition of civilization..
The Pax Romana (Roman Peace) was a time of peace and prosperity hitherto unknown and it would last For over 200 years. Augustus ruled the empire from 31 BCE until 14 CE when he died. In that time, as he said himself, he found Rome a city of clay but left it a city of marble..