  Machines enabled the Industrial Revolution and are central to modern
technological progress: A machine's parts transmit forces, motion, and energy
to one another in a predetermined manner. Today's engineering frontier,
building artificial micromachines that emulate the biological machinery of
living organisms, requires faithful assembly and energy consumption at the
microscale. Here, we demonstrate the programmable assembly of active particles
into autonomous metamachines using optical templates. Metamachines, or machines
made of machines, are stable, mobile and autonomous architectures, whose
dynamics stem from the geometry. We use the interplay between anisotropic force
generation of the active colloids with the control of their orientation by
local geometry. This allows autonomous reprogramming of active particles of the
metamachines to achieve multiple functions. It permits the modular assembly of
metamachines by fusion, reconfiguration of metamachines and, we anticipate, a
shift in focus of self-assembly towards active matter and reprogrammable
materials.
