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The recent high-pressure synthesis of pentazolates and the subsequent stabilization of the aromatic [N₅]⁻ anion at atmospheric pressure have had an immense impact on nitrogen chemistry. Other aromatic nitrogen species have also been actively sought, including the hexaazabenzene N₆ ring. Although a variety of configurations and geometries have been proposed based on ab initio calculations, one that stands out as a likely candidate is the aromatic hexazine anion [N₆]⁴⁻. Here we present the synthesis of this species, realized in the high-pressure potassium nitrogen compound K₉N₅₆ formed at high pressures (46 and 61 GPa) and high temperature (estimated to be above 2,000 K) by direct reaction between nitrogen and KN₃ in a laser-heated diamond anvil cell. The complex structure of K₉N₅₆—composed of 520 atoms per unit cell—was solved based on synchrotron single-crystal X-ray diffraction and …