Rome has passed through the Republican and then Imperial eras to the Middle Age, Renaissance, Baroque, and Rococo, classicism, and modern periods. Each of thse stages has influenced the development of the city. The settlement of Rome started on the Palatine Hill. It was there that the walled original cell that the Romans called Roma Quadrata was built, according to Varro, in 753 BC. Iron age huts have been found, including the so called House of Romulus, that can be dated to the ninth-century BC by their funerary urns. In 509 BC the Roman republic was founded and based in Rome. In 313 AD under the reign of Emperor Constantine (r. 306-337) Rome became the official centre of Christianity. Constantine founded Constantinople as the capital of the eastern part of the Roman Empire. Consequently, it emerged as a revival to Rome. Over time, the Roman Empire began to weaken and in 476 the German tribes that inhabited the northern borders of the empire brought the Roman Empire to its end.