Crow's nest was named in 18th century as such, but the concept existed well into the past.
Probably since most ancient times, when first ships started to be build, as the idea is very natural for descendants of tree climbing monkeys.
The higher you are - the farther you can see.
Besides +2 sight is too good.
Galleon already has pretty wide range of sight and recently navigation was added with +1 sight as well.