Along with prehistoric architecture, the Greeks and Etruscans were the first people in Italy to actually establish a succession of styles. The Etruscans were the architects who led the way in Northern and Central Italy at the period. Etruscan structures were built of brick and wood... which deteriorated over time. The Greeks on the other hand used marble for their buildings which survived much longer. The Romans adopted many architectural elements from the Greeks (such as pillars and doorways) but also developed some original ideas of their own. For example, they are responsible for the introduction of concrete into Europe. Concrete has many advantages over stone or brick because it is easy to work with and durable too. It can be colored and decorated in all kinds of ways so the Roman's made beautiful walls, floors and ceilings using this material. When Rome fell in A.D. 400 the Italian region became divided up between different kingdoms and cities which resulted in different architectural styles developing across the country. By the 9th century Siena had become so powerful it managed to win independence from the Byzantine Empire and its new government hired an architect named Abu Salih al-Karkhi to design and build a new city. Al-Karkhi created something new: a mix of Arab and European styles. He used red clay for the foundations of his houses instead of stone like the Etruscans did, and he also added windows and balconies which were unusual at that time.