Carbon disulphide (CS2) is, together with its closest analogue CO2, one of the simplest molecular systems made of double covalent bonds. Under high pressure, the molecular structure is expected to break up to form extended crystalline or polymeric solids. Here we show that by compression at 300 K to ∼10 GPa (100 kbar) using large-volume high pressure techniques, a sudden reaction leads to a mixture of pure sulphur and a well-defined compound with stoichiometry close to C2S which can be recovered to ambient pressure. We present neutron and x-ray diffraction as well as Raman data which show that this material consists of sulphur bonded to sp2 graphite layers of nanometric dimensions. The compound is a semiconductor with a gap of 45 meV, as revealed by temperature dependent resistivity measurements, and annealing at temperatures above 200 °C allows to reduce its sulphur content up to C10S. Its structural and electronic properties are fundamentally different to “Bridgman black” reported from previous high pressure experiments on CS2.