The Rus’ Castle Turret emplacement for their Wooden Fortress gives the same visuals as the Arrowslits that are displayed on every other Outpost in the game. Getting the Arrowslit upgrade also gives that visual for Rus.
This makes it less visually conherent for players who are used to seeing that Arrowslits model appear upon getting it. Meaning players facing against Rus’ Wooden Fortress need to check their stats to see if they even have Arrowslits before safely approaching it; which is unlike every other Civilization in the game.
I figure this must be a bug, because it encroaches on Arrowslit’s established design.