The major survivals of Buddhist art begin in the period after the Mauryans, from which good quantities of sculpture survives. Some key sites are Sanchi, Bharhut and Amaravati, some of which remain "in situ", with others in museums in India or around the world. Stupas were surrounded by ceremonial fences with four profusely carved toranas or ornamental gateways facing the cardinal directions. These are in stone, though clearly adopting forms developed in wood. They and the walls of the stupa itself can be heavily decorated with reliefs, mostly illustrating the lives of the Buddha. Gradually life-size figures were sculpted, initially in deep relief, but then free-standing. Mathura was the most important centre in this development, which applied to Hindu and Jain art as well as Buddhist. The facades and interiors of rock-cut "chaitya" prayer halls and monastic "viharas" have survived better than similar free-standing structures elsewhere, which were for long mostly in wood. The caves at Ajanta, Karle, Bhaja and elsewhere contain early sculpture, often outnumbered by later works such as iconic figures of the Buddha and bodhisattvas, which are not found before 100 CE at the least.