widely admired schools. In the second century AD, The Roman emperor Hadrian, himself an Athenian citizen, ordered the construction of a library, a gymnasium, an aqueduct which is still in use, several temples and sanctuaries, a bridge and financed the completion of the Temple of Olympian Zeus. By the end of Late Antiquity, Athens had shrunk due to sacks by the Herulians, Visigoths, and Early Slavs which caused massive destruction in the city. In this era, the first Christian churches were built in Athens, and the Parthenon and other temples were converted into churches. Athens expanded its settlement in the second half of the Middle Byzantine Period, in the ninth to tenth centuries AD, and was relatively prosperous during the Crusades, benefiting from Italian trade. After the Fourth Crusade the Duchy of Athens was established. In 1458, it was conquered by the Ottoman Empire and entered a long period of decline. Following the Greek War of Independence and the establishment of the Greek Kingdom, Athens was chosen as the capital of the newly independent Greek state in 1834, largely because of historical and sentimental reasons. At the time, after the extensive destruction it had suffered during the war of independence, it was reduced to a town of about 4,000 people (less than half its earlier population) in a loose swarm of houses along the foot of the Acropolis. The first King of Greece, Otto of Bavaria, commissioned the architects Stamatios Kleanthis and Eduard Schaubert to design a modern city plan fit for the capital of a state. The first modern city plan consisted of a triangle defined by the Acropolis, the ancient cemetery of Kerameikos and the new palace of the Bavarian king (now housing the Greek Parliament), so as to highlight the continuity between modern and ancient Athens. Neoclassicism, the international style of this epoch, was the architectural style through which Bavarian, French and Greek architects such as Hansen, Klenze, Boulanger or Kaftantzoglou designed the first important public buildings of the new capital. In 1896, Athens hosted the first modern Olympic Games. During the 1920s a number of Greek refugees, expelled from Asia Minor after the Greco-Turkish War and Greek genocide, swelled Athens's population; nevertheless it was most particularly following World War II, and from the 1950s and 1960s, that the population of the city exploded, and Athens experienced a gradual expansion. In the 1980s, it became evident that