Adding custom structure to replace ancient_city_center

Question

I would like to have a custom structure I made replace the city_center structure of an ancient city, except when I do that, cities do not generate at all.

To make sure it was working, I replaced the tall_ruins structures instead, and then cities did generate again, but then those ruins did not generate.

What am I doing wrong? How do I replace one part of a city?

Answer 1

Edit: So apparently it was due to my structure not having a jigsaw setting the city center. At that point my structure generated, but not the rest of the city. The solution? More jigsaws.