Structures built a millenia ago by the Guardians, a faction within the Temporal Cold War, to slowly convert normal space to the laws of physics more hospitable to their species as a prelude to invasion. At least 59 Spheres are identified: typically 19 km in diameter, they are built of a single alloy and stay hidden within a cloaking field 70,000 km wide. Powered by seven fusion reactors some 12 km long, each Sphere emits gravimetric waves that cause spatial anomalies at the points where their emissions intersect.