How was length measured long ago?

In which country? The Metric System was invented in post-Revolutionary France to replace a vast and utterly chaotic collection of trade-invented units, often varying regionally.

'

Britain used the Imperial system (inch, foot, pound-avoirdupois, gallon, etc), and that spread to America and many other countries, albeit with some changes such as the difference between UK and US gallon. Other countries had their own units: I found one used the delightfully named "pood" for mass, but I don't know which!

'

Nowadays the Systeme Internationale version of the Metric System is used world-wide, both nationally and internationally, for trade, sports, science and engineering.