Singidunum
Singidunum is the name for the ancient city in Serbia which became Belgrade, the capital of Serbia. It was recorded that a Celtic tribe, the Scordisci, settled the area in the 3rd century BC following the Gallic invasion of the Balkans. The Slavic Beligrad, the "white city" (named for the color of the stone it was built from), had been established by the 9th century on the site of Singidunum, within the First Bulgarian Empire. It is first mentioned in a letter written on 16 April 878 by Pope John VIII to Bulgarian prince Boris I Mihail.