Short answers, pulled from the story.
Roman soldiers established a military camp called Vindobona on the site of today's Vienna city centre around AD 97. Construction of this legionary fort began to secure the borders of the Roman Empire in the province of Pannonia.
Leopold I of Babenberg became Margrave of the Eastern March in 976, establishing a frontier district along the Danube that would evolve into Austria. Henry II, Duke of Austria, moved his residence from Klosterneuburg to Vienna in 1155, coinciding with the founding of the Schottenstift monastery.
Ottoman forces advanced toward Vienna on two notable occasions: the Siege of Vienna in 1529 and the Battle of Vienna in 1683. Both attempts resulted in successful defense of the city against Turkish armies.
In 1679, the Great Plague struck Vienna, claiming nearly one-third of its inhabitants and devastating the population. The event occurred before the Habsburgs established Vienna as the seat of emperors of the Holy Roman Empire in the 16th century.
Adolf Hitler arrived in Vienna on the 15th of March 1938, three days after German troops entered Austria. Persecution of Jews began almost immediately as Viennese homes and businesses were plundered, and all synagogues and prayer houses in the city were destroyed except for the Stadttempel due to its proximity to residential buildings.
The Austrian State Treaty was signed in May 1955 and came into force on the 27th of July 1955. By October, all foreign soldiers had left the country following ten years of occupation divided among four powers.