Triads and triangles
Barrocal dolmen, close to Tourega (Évora).
The uprights seem to be intentionally shaped, on the upper edge, to suport the capstone on a single point.
Whatever the intention, the result is a series if triangular gaps between the uprights and the capstone...
Originally, those gaps were certainly filled with a drystone structure, so keeping them clearly distinct from the rest of the walls.