Vindobona is the name of a Roman army camp - built on the site of a Celtic settlement - which formed the foundation of (and eventually grew into) Vienna, the capital of Austria.
Vindobona was built in the early 1st century CE under the rule of Tiberius, the stepson of the emperor Augustus. The first mention of the camp in Roman literature occurs in Pliny's encyclopedia (published around 77 CE); Pliny calls it Vianiominia, although the inscriptions extant at the site use only the later form Vindobona. It was a camp of some importance; at various times, the legions X, XIII, and XIV (all titled "Gemina") used it as a base, and the emperor Marcus Ulpius Traianus used it as a forward base for his campaign in Dacia. Marcus Aurelius is said to have stayed frequently at the camp during his campaigns against the Marcomanni; he died there of plague in the year 180 CE.
Vindobona declined during the mass migrations of German tribes during the 4th and 5th centuries CE, as Roman authority in the area weakened and collapsed. There is archaeological evidence of a disastrous fire in the camp's storage area during the early 5th century, and in the year 433 CE the emperor Theodosius gave up the entire region to Hunnic invaders without a fight. There are few records to indicate the area's fate during the so-called "Dark Ages," but the site reappears in the Chronicles in 791 CE, when Charlemagne seized control of the region. The camp's fortifications continued to exist into the 13th century, and the course of its walls can still be seen via the street layout in Vienna's inner city, so it is clear that some manner of settlement remained in the area throughout the unrecorded period.
Vindobona was initially built to the standard plan for a Roman military fort, or castrum - a square fortification with each wall pierced in the middle by a single gate; it was protected on one side by the Danube and on others by a moat. The camp had heated baths and, eventually, a well-constructed canal system; it is believed to have harbored up to 20,000 people at times. There is also evidence of a civilian settlement to the southeast, about which very little is known.
The camp was located directly beneath the center of the oldest part of Vienna, again suggesting continuous settlement in the region throughout the Common Era. The remains of the Vindobona were first rediscovered in the 19th century, although most of the serious excavation did not take place until the mid-20th. A portion of it can be viewed today - part of two houses from the earliest period of the camp, which had some pretty impressive provisions for underfloor heating. It's a relatively small area, but is well worth seeing - it's pretty awe-inspiring to look at the ancient underpinnings of one of Europe's greatest cities. The entrance is on Hoher Markt, facing the fountain Vermählungsbrunnen; it's kind of hard to see, and is inside a large metal-and-glass building. Look for signs that say "Romisch ruins." Another section of the camp is exposed near the grand entrance to the imperial palace - the streets have been peeled back in successive layers to show construction from different eras, including a 14th century arcade, Roman canals, and the remains of another house of Vindobona (which still has fragments of fresco clinging to the wall.) Again - see it if you can.
Incidentally, Vindobona is mentioned in the film Gladiator, as the site of Maximus' final battle and Marcus Aurelius' death. A nice touch.
I used information from the Vienna tourist information web site, the Oxford Classical Dictionary, the Penguin Historical Atlas of Ancient Rome, Richard Jaklitsch's "The History of Austria," the Catholic Encyclopedia's entry on Vienna, and the official Vienna web site in the preparation of this summary.