alt Hacker NewsThat's the problem with going too far using "money" or "GDP" - you can roughly compare the WWII 45% of GDP spent with today - https://www.davemanuel.com/us-defense-spending-history-milit... because even by WWII much was "financialized" in such a way that it appears on GDP (though things like victory gardens, barter, etc would explicitly NOT be included without effort - maybe they do this?).
As you get further and further into the past you have to start trying to measure it using human labor equivalents or similar. For example, what was the cost of a Great Pyramid? How does the cost change if you consider the theory that it was somewhat of a "make work" project to keep a mainly agricultural society employed during the "down months" and prevent starvation via centrally managed granaries?
You don't even need to go that far back to run into issues, when I read Pride and Prejudice, I think Mr. Darcy was one of the richest people in England at around £10,000/year, but if you to calculate his wealth in today's terms it wasn't some outrageous sum (Wikipedia is telling me ~£800,000/year). The thing is that the economy was totally different back then -- labor cost practically nothing, but goods like furniture for instance were really expensive and would be handed down for generations.
With £800K today, you may not even be able to afford the annual maintenance for his mansion and grounds. I knew somebody with a biggish yard in a small town and the garden was ~$40K/yr to maintain. Definitely not a Darcy estate either.
Thinking about it, an income of £800K is something like the interest on £10m.