I’d assume they had animals to graze the lawn but that seems like it would be a long process and it wouldn’t be thorough throughout the whole lawn.
Hi, lawns weren't much of a thing "back in the day"; here are some previous posts on the history of lawns and the inevitable lawn maintenance
/u/rosstafarii provides a quick background in Did the French aristocracy really invent the idea of having a lawn?
/u/shayeraaa picks things up in the late 18th c in What is the history of the front lawn?
and finally, a more focussed discussion on cutting the grass in When did "trimmed-lawns" become a popular thing? , which covers more recent history in the UK and US