One gold piece (soldius) was probably worth about one month’s wage for a soldier, and or basic food for six to nine months. So the cost of this church was about the price to maintain a legion of soldiers for half a year. If we assume a soldius is worth six months of meals, at $10/day, which is about what I spend for food (you have to cook for yourself), then the cost of San Vitale is about $50 million today. St. Paul’s Cathedral in London cost about $80 million in today’s currency, so I guess $50 million is reasonable; San Vitale is much smaller.

That still sounds cheap to me, I figured a cathedral would start at $1 billion. If I ever get $50 million, I think I’ll build a beautiful cathedral!