If you’re confused about fortifications being at Waterloo, this is referring to the walled manor house that was used as a forward position. The Hugoumont:

https://en.m.wikipedia.org/wiki/Hougoumont

Back in the day, the Soviet Red army trained 16,000 troops in Napoleonic cavalry, infantry, and artillery tactics for a film version of ‘War and Peace.’ Hollywood rented those troops for ‘Waterloo.’ They made a detailed study of the battle and literally built a replica from the ground up, including the roads.

If you want to see an excellent reproduction of the battle see this movie.

Clip

https://youtu.be/97dBfdNrf9A