Contemporary name Bratislava originates from Šafárik's philological reconstruction of its medieval name.

"The modern Slovak name Bratislava, however, is assumed to be derived (by mistake) from the name of the Czech ruler Bretislav I."
So you should return name to Preslava, since Šafarik made mistake :D

[size=14pt]Banja Luka or Banjaluka, capital of Republika Srpska[/size]

Several localities around city, from ancient times (Illyrians, Celts, Romans), there is a substantial evidence of the Roman presence in the region during the first few centuries A.D., including an old fort "Kastel" (Castra, lat.) in the centre of the city Banja Luka.

1224. First time mention Vrbaski grad (city on river Vrbas, were modern Banja Luka is)
1494. 6th February, first mention of Banja Luka in the Charter of the Hungarian king Vladislav II Jagiellonian, name interpreted as Ban's (military title) meadow.

"The identity of the ban and the meadow in question remain uncertain, and popular etymology combines the modern words banja ("bath" or "spa"), or bajna ("marvelous") and luka ("port"). A different interpretation is suggested by the Hungarian name "Lukácsbanya", i.e. "Luke's Mine", which is also the meaining of Slovak "Banja Luka"."