I know, it is staggering to think what they achieved so much with just some maths and a lot of brute force.

The people back then did know a hell of a lot more than later generations until as you say the 1700's and a little earlier.
The knowledge of math and perspective was 'rediscovered' during the renaissance in the 15th century.
It shows us that there have been times when humanity seems to go backwards in terms of knowledge?