It's the wonder of the Anglo-Saxons, Church of Brixworth
https://en.wikipedia.org/wiki/All_Saints'_Church,_Brixworth
https://wildfiregames.com/forum/topic/22783-1000-anglo-saxons-all-saints-church-brixworth-wonder/#comment-336603
I made an excel with all units
For me is not because "it is difficult," but civs like Athenians or Spartans even they are really strong, cavalry is faster.