Short answers, pulled from the story.
Pannonia Superior was a Roman province formed in 103 AD from the division of the older province of Pannonia, with Carnuntum as its capital. Its territory overlapped modern-day Hungary, Croatia, Austria, Slovakia, and Slovenia.
Septimius Severus made his bid for the Roman imperial throne in April 193 CE while serving as governor of Pannonia Superior.
In 308, Emperor Diocletian chaired a meeting with co-emperors Maximian and Galerius in Carnuntum to resolve tensions within the Tetrarchy. On the 11th of November 308, Galerius appointed Licinius as Augustus in place of Valerius Severus, who had died at the hands of Maxentius, and ordered Maximian to step down permanently.
Diocletian refused, saying: "If you could show the cabbage that I planted with my own hands to your emperor, he definitely wouldn't dare suggest that I replace the peace and happiness of this place with the storms of a never-satisfied greed."
Pannonia Superior's cities included Vindobona, today Vienna in Austria; Siscia, today Sisak in Croatia; Savaria, today Szombathely in Hungary; Scarbantia, today Sopron in Hungary; Arrabona, today Győr in Hungary; and Poetovio, today Ptuj in Slovenia, among others.
The name Upper Pannonia carried on into the 8th-century Frankish March of Pannonia, applied to its northern part. In the 12th century, the chronicler Otto von Freising used the same name to refer to Austria.