Some of the first and most influential figurative portrayals of the Buddha appeared at this time, perhaps modelled on Greek statues of Apollo in the Greco-Buddhist style. Several Buddhist traditions may have been influenced by the ancient Greek religion: the concept of Boddhisatvas is reminiscent of Greek divine heroes, and some Mahayana ceremonial practices (burning incense, gifts of flowers, and food placed on altars) are similar to those practised by the ancient Greeks; however, similar practices were also observed amongst the native Indic culture. One Greek king, Menander I, probably became Buddhist, and was immortalized in Buddhist literature as 'Milinda'. The process of Hellenization also spurred trade between the east and west. For example, Greek astronomical instruments dating to the 3rd century BC were found in the Greco-Bactrian city of Ai Khanoum in modern-day Afghanistan, while the Greek concept of a spherical earth surrounded by the spheres of planets eventually supplanted the long-standing Indian cosmological belief of a disc consisting of four continents grouped around a central mountain (Mount Meru) like the petals of a flower. The Yavanajataka (lit. Greek astronomical treatise) and Paulisa Siddhanta texts depict the influence of Greek astronomical ideas on Indian astronomy.