Linked from
The 30 pages that link to Riemannian geometry, each with the reason it gives.
Metric tensorNarrower topic: This field takes the metric tensor as its basic geometric structure.
Riemann curvature tensorNarrower topic: The tensor is a central invariant of this geometric theory.
Hopf–Rinow theoremNarrower topic: The theorem became a foundational result in this field.
Shape of the universeNarrower topic: It provides the language for describing curved spatial slices.