@feneur know maybe. My understanding is that it was done to show their defensive and otarcist nature. I believe it's somewhere on the design document
See also https://trac.wildfiregames.com/wiki/ArtDesignDocument#CultureHistoryandRealism
https://trac.wildfiregames.com/wiki/Civ%3A_Iberians#CIVBONUSES http://docs.wildfiregames.com/design/
Actually it's on every single skirmish map. It's a skirmish entity. For Random maps you're right, it's part of the code.