developed during the republican years (509–27 BC), modified from Greek and Etruscan prototypes. Wherever the Roman army conquered, they established towns and cities, spreading their empire and advancing their architectural and engineering achievements. While the most important works are to be found in Italy, Roman builders also found creative outlets in the western and eastern provinces, of which the best examples preserved are in modern-day North Africa, Turkey, Syria and Jordan. Extravagant projects appeared, like the Arch of Septimius Severus in Leptis Magna (present-day Libya, built in 216 AD), with broken pediments on all sides, or the Arch of Caracalla in Thebeste (present-day Algeria, built in 214 AD), with paired columns on all sides, projecting entablatures and medallions with divine busts. Due to the fact that the empire was formed from multiple nations and cultures, some buildings were the product of combining the Roman style with the local tradition. An example is the Palmyra Arch (present-day Syria, built in 212–220), some of its arches being embellished with a repeated band design consisting of four ovals within a circle around a rosette, which are of Eastern origin. Surpassing most civilisations of their time, the Romans developed new engineering skills, architectural techniques and materials. Among the many Roman architectural achievements were domes (which were created for temples), baths, villas, palaces and tombs. The most well known example is the one of the Pantheon in Rome, being the largest surviving Roman dome and having a large oculus at its centre. Another important innovation is the rounded stone arch, used in arcades, aqueducts and other structures. Besides the Greek orders (Doric, Ionic and Corinthian), the Romans invented two more. The Tuscan order was influenced by the Doric, but with un-fluted columns and a simpler entablature with no triglyphs or guttae, while the Composite was a mixed order, combining the volutes of the Ionic order capital with the acanthus leaves of the Corinthian order. Between 30 and 15 BC, the architect and engineer Marcus Vitruvius Pollio published a major treatise, De architectura, which influenced architects around the world for centuries. As the only treatise on architecture to survive from antiquity, it has been regarded since the Renaissance as the first book on architectural theory, as well as a major source on the canon of classical architecture. Just like the Greeks, the Romans built amphiteatres too. The largest amphitheatre ever built, the Colosseum in Rome, could