And then there's the mile. Originally comes from the Latin for a thousand (mille) paces, and one pace being 5 foot, so a mile used to be 5000 feet. But now it's a beautifully round 5280 feet. How come?

Well, in the middle ages, the furlong was important, because it was the standard size for farmers' fields (based on how long a furrow an ox could plow without resting). But 8 furlongs didn't fit neatly into a mile, so to make things easier for everybody, the mile got expanded to a nice round 5280 feet, or exactly 8 furlongs.