That is perfectly standard German!You should be able to find the words in any German dictionary.
You have a spelling error.The correct spelling of the first city you mention is Schäßburg -- or if written without the "Umlaut" (two dots) over the "a", and without the German character "scharfes S" (ß) -- Schaessburg.
Schäßburg (Schaessburg) is called in Romanian Sighisoara.
The second city you mention, the city called in Romanian Sibiu, is called in German Hermannstadt.
I assume that you are aware that these cities are located in the region known as TRANSYLVANIA (in German: Siebenbürgen, or if written without the "Umlaut" or two dots over the "u", Siebenbuergen), which until 1918, was part of Hungary.Following World War I, Transylvania was awarded to Romania.
Transylvania having been part of Hungary until 1918, the two cities you mention also have Hungarian names:The city called in German Schäßburg (Schaessburg) and in Romanian Sighisoara, is called in Hungarian Segesvár.The city called in German Hermannstadt and in Romanian Sibiu, is called in Hungarian Nagyszeben.