From drug delivery(1,2) to chemical and biological catalysis(3) and cosmetics(4), the need for efficient fabrication pathways for particles over a wide range of sizes, from a variety of materials, and in many different structures has been well established(5). Here we harness the inherent scalability of fibre production(6) and an in-fibre Plateau-Rayleigh capillary instability(7) for the fabrication of uniformly sized, structured spherical particles spanning an exceptionally wide range of sizes: from 2 mm down to 20 nm. Thermal processing of a multimaterial fibre(8) controllably induces the instability(9), resulting in a well-ordered, oriented emulsion(10) in three dimensions. The fibre core and cladding correspond to the dispersed and continuous phases, respectively, and are both frozen in situ on cooling, after which the particles are released when needed. By arranging a variety of structures and materials in a macroscopic scaled-up model of the fibre, we produce composite, structured, spherical particles, such as core-shell particles, two-compartment 'Janus' particles(11), and multi-sectioned 'beach ball' particles. Moreover, producing fibres with a high density of cores allows for an unprecedented level of parallelization. In principle, 10(8) 50-nm cores may be embedded in metres-long, 1-mm-diameter fibre, which can be induced to break up simultaneously throughout its length, into uniformly sized, structured spheres.