Foundations have lower resistances than finished structures, making them easier to destroy. However, the current resistance levels of foundations seem a bit arbitrary:
h , p , c : 4, 7, 3: Siege Walls 3, 15, 3: Civic Centre 3, 10, 3: Embassy; Special structures 2, 10, 2: Wonder 1, 10, 1: Assembly, Corral, Field 1, 5, 1: Army Camp; Civic, Defensive, Economic, Military structures 1, 1, 1: other structures
Having the foundations of e.g. city walls and fortresses (at 1, 5, 1) much easier to destroy than those of siege walls (4, 7, 3) or embassies (3, 10, 3) doesn't make that much sense.
This patch unifies the resistances of the foundations of all structures, to 1, 10, 1, which means a foundation of X health is as easy to destroy as a foundation of X health of any other structure, making things more predictable for players, as well as easier to understand and balance, and having lines in far fewer files.