The orders, structural systems for organising component parts, played a crucial role in the Greeks' search for perfection of ratio and proportion. The Greeks and Romans distinguished three classical orders of architecture, the Doric, Ionic, and Corinthian orders; each had different types of capitals atop the columns of their hypostyle and trabeate monumental buildings. Throughout the Mediterranean Basin, the Near East, and the wider Hellenistic world including the Greco-Bactrian Kingdom and the Indo-Greek Kingdom, numerous variations on these and other designs of capitals co-existed with the regular classical orders. The only architectural treatise of classical antiquity to survive is De architectura by the 1st-century BC Roman architect Vitruvius, who discussed the different proportions of each of these orders and made recommendations for how the column capitals of each order were to be constructed and in what proportions. In the Roman world and within the Roman Empire, the Tuscan order was employed, originally from Italy and with a capital similar to Greek Doric capitals, while the Roman imperial period saw the emergence of the Composite order, with a hybrid capital developed from Ionic and Corinthian elements. The Tuscan and Corinthian columns were counted among the classical canon of orders by the architects of Renaissance architecture and Neoclassical architecture.