The medieval settlement is known in modern sources as Blatnohrad (Slovak), Blatnograd, Блатноград (Serbo-Croatian and Bulgarian).

In the 9th century, Mosapurc or Moosburg[4] was a fortified settlement built along the Zala river and was the capital of the Frankish vassal Lower Pannonian Principality ruled by a Slavic prince Pribina ("Privinae civitas, munimen, castrum in nemore et palude Salae" in a Salzburg chronicle).

They and their disciples turned Blatnograd into one of the centers that spread the knowledge of the new Slavonic script (Glagolitic alphabet) and literature, educating numerous future missionaries in their native language.

It is claimed that Urbs Paludarum, Brazlavo's burg (Moosburg), was the site of the Battle of Pressburg, instead of Bratislava.

[6] According to the annals, the battle took place in the vicinity of Brezalauspurc, the castle of Duke Brazlavo (Braslav), located west of Lake Balaton.