The Moscow Kremlin is at once a fortress, a religious centre and the seat of a state. Its triangular circuit of red brick walls and towers was rebuilt at the end of the 15th century by Italian architects summoned to Moscow, who married Renaissance military engineering to Russian tradition. Within lies Cathedral Square, where the Dormition, Archangel and Annunciation cathedrals stand together beneath the Ivan the Great Bell Tower: coronations, burials and the great ceremonies of the Russian state all took place in this compact space. Palaces, armouries and treasuries complete the ensemble, inscribed with Red Square on the UNESCO World Heritage List. Filmed in 4K from the river, the walls and the air, the programme reads the Kremlin as architecture and as an unbroken centre of political gravity.