Curving bones: On larger length scales, bone is known to have a hierarchical structure in which small crystals of calcium phosphates arrange themselves around helices of collagen. These make up larger structures, such as the osteons found in compact bone. However, at smaller lengths, does the hierarchical structure persist? By combining three-dimensional electron tomography with two-dimensional electron microscopy, Reznikov et al. observed structural ordering from the nanoscale upward. At the smallest scale, needle-shaped mineral units form platelets that organize into stacks bridging multiple collagen units. Science , this issue p. eaao2189

• Twisting of structural elements of bone can be found across multiple scales. • 3D imaging and analysis supports original observations by Pettigrew and Thompson. • Self-similarity in the form of the twist is a hallmark of bone structure. • Consideration of twisting/spiraling in bone may enhance understanding of function.