Vienna was originally a Celtic city founded around 500 BC. In 15 BC, it became a frontier city ("Vindobona") guarding the Roman Empire against the German tribes to the north. In the Middle Ages, it became the home of the Babenberg and, later, the Habsburg dynasties and through the latter the capital of the Holy Roman Empire and later the Austro-Hungarian Empire. The Ottoman Turkish invasions of Europe in the 16th and 17th centuries were stopped two times in total at Vienna. See the Battle of Vienna (1683). In 1815, Vienna was the site of the Congress of Vienna which redrew national boundaries in Europe after the defeat of Napoleon Bonaparte at Waterloo.During the Cold War, Vienna was a hotbed of international espionage owning to its location in neutral Austria, between the Western and Eastern blocs.Other famous Viennese features include the Lipizzaner stallions of the Spanish Riding School, the Vienna Boys' Choir (Wiener Sängerknaben), Wiener Schnitzel, Sachertorte, and various pastries. Viennese cafes claim to have invented the process of filtering coffee from the captured baggage after the second Turkish siege of 1683.