From Stamps of the World
Rijeka (Italian and Hungarian: Fiume) is the principal seaport and the third-largest city (128,624 inhabitants in 2011) in Croatia (after Zagreb and Split). It is located on Kvarner Bay, an inlet of the Adriatic Sea. Historically, because of its strategic position and its deep-water port, the city was fiercely contested, especially among Italy, Hungary, and Croatia.
Postmark in Croatia
Postmark in Yugoslavia
Postmarks in the Kingdom of Croatia-Slavonia (1868-1918)
In practice, postally administered by the Kingdom of Hungary.
Sušak (Porto Barros) is a the eastern part of the city of Rijeka.
Postmarks in Austrian Empire Croatia-Slavonia province
The FIUME post office opened before 1850.