Many worked for the organized Church and were in holy orders (like Petrarch), while others were lawyers and chancellors of Italian cities, like Petrarch's disciple, Salutati, the Chancellor of Florence, and thus had access to book copying workshops. One of the most remarkable poets of the early 19th and 20th century writers was Giacomo Leopardi, who is widely acknowledged to be one of the most radical and challenging thinkers of the 19th century. Italo Svevo, the author of "La coscienza di Zeno" (1923), and Luigi Pirandello (winner of the 1934 Nobel Prize in Literature), who explored the shifting nature of reality in his prose fiction and such plays as "Sei personaggi in cerca d'autore" ("Six Characters in Search of an Author", 1921). Federigo Tozzi and Giuseppe Ungaretti were well-known novelists, critically appreciated only in recent years, and regarded one of the forerunners of existentialism in the European novel. Since the Roman Empire, most western contributions to Western legal culture was the emergence of a class of Roman jurists. During the Middle Ages, St. Thomas Aquinas, the most influential western scholar of the period, integrated the theory of natural law with the notion of an eternal and biblical law. During the Renaissance, Prof. Alberico Gentili, the founder of the science of international law, authored the first treatise on public international law and separated secular law from canon law and Roman Catholic theology. Enlightenment's greatest legal theorists, Cesare Beccaria, Giambattista Vico and Francesco Mario Pagano, are well remembered for their legal works, particularly on criminal law. Francesco Carrara, an advocate of abolition of the death penalty, was one of the foremost European criminal lawyers of the 19th century. During the last periods, numerous Italians have been recognised as the prominent prosecutor magistrates. Italians have been the central figures of countless inventions and discoveries and they made many predominant contributions to various fields. During the Renaissance, Italian polymaths such as Leonardo da Vinci (1452–1519), Michelangelo (1475–1564) and Leon Battista Alberti (1404–72) made important contributions to a variety of fields, including biology, architecture, and engineering. Galileo Galilei (1564–1642), a physicist, mathematician and astronomer, played a major role in the Scientific Revolution.