There was a movie, with the crosses in the castle walls - darned if I can remember it.
Most castle wall built prior to the general use of firearms had portrals in the shape of crosses. The cross shape allowed the use of bows and crossbows at different angles ie: up or down, left or right. In military speak: “fields of fire”. Still used to this day with adaptations to modern weapons. A days drive in England will show you the whole array to include WWII “pillboxes” along some rural highways.
Looks to me as if the “cross” could just be the result of one horizontal stone breaking and falling out. Look sideways from the cross to the place with 2 holes near the left edge of the picture.
Thanks patton.