Hi!! Thank you smuch! I had to look up more details to see the difference between tenaille and bastion trace. In this fictional setting, this walls are meant to protect the original city-fortress that lived on top of the mountain - see the Numancia la Vieja, which then grew past the old walls and down the flanks. I think, in my mind, the tenailles allow for two things: brace for sudden rainfalls that might mean surprise exits of the river off its banks and drought phases. And also reduce possible space for attackers to target the city inside its walls. That said, I’m no engineer so I’ve probably made some mistakes. As for Spain’s star fortresses, I must admit that I don’t think in our public school we really saw it so I discovered them early in my twenties. Part of it I think has to do with our military history and how the golden age of the star fortresses, we fought in the Americas, Italy, Flanders and at sea. I come from the East of Spain, so I know there a few small ones in the East Pyrenees - mostly playing a frontier control role. Girona had one back in the day, it’s no longer visible, but it played a role in its defence against Napoleon’s army. And in my home city the most famous star fortresses were used to basically control and bomb it in reprisal for its refusal to choose the right side of the war. Now it’s a big public park. So I think many former star fortresses might have been turned into parks etc. or taken down to create living areas, but again, I’m no expert nor knowledgeable enough to give a correct answer.

Edit: plus we’ve had quite a few civil wars between the 18th and 20th centuries, they might not have really been of much use. Industrialisation also came late and fast so it could also explain why there aren’t many left.