In the 4th century, after having the Valcum Fortress built, the neighborhood of Keszthely became populous. A castrum built on piles and surrounded by marshland was presumably built in the area of Zalavár at that time. During the period of migration, it was occupied by several nations; it was in the possession of the eastern Goths, Lombards, Huns and Franks.
In the 840s, it was enfeoffed to the dislodged Slavic suzerain, Pribina (Privina), then later he inherited the marshland located at the meeting point of Zala River and Lake Balaton. According to eastern Frankish sources, he had a castle built in place of the former castrum, which he called Mosaburg (Blatengrad in ancient Slavic, Blatnohrad in Slovakian, meaning: "Marsh Castle"). The Slavic suzerain made Mosaburg the center of his country. According to historians, the castle of Pribina is not the same as Moosburg in Carinthia, but could stand in the area of today’s Zalavár. (The legendary fortress is also mentioned by István Fekete’s novel titled Tüskevár but its exact place is not known today.)
The first church of Mosaburg was built in 850 in honor of Maria and was sanctified by Liutprand, the archbishop of Salzburg. Later on additional churches were also built during the reign of Pribina and his successor, Kocel. The latter suzerain housed monks Cyril and Method in his court. After the death of Kocel in 876, Mosaburg got to the hands of the Franks again. According to a description from 885, the palisade castle was in the ownership of the archbishop of Salzburg but it remained one of the cultural centers of Slavs.
Eventually, the Hungarians occupied the city around 900, named it Zalavár and transformed it into one of their important centers. Natives looked for a living in the neighborhood, thus in the 10th century an individual culture arose from the mixture of the Hungarian and Slavic population in this area.
In Saint Stephen’s system of hundreds Zalavár became the center of the populous Zala hundred. In 1019, a new basilica and Benedictine monastery were built, which was the owner of the settlement as of its foundation. The first source talking about the ranking of the cloister seat of Zalavár was in 1137. The castle is mentioned for the first time in 1164, and then in 1222, it is again written about as a royal estate.
The castle that was reinforced in 1420 became the property of the Rozgonyi Family by the middle of the 15th century. In the meantime, the settlement continuously increased its significance: it received the right to hold national markets in 1424 and to hold weekly markets in 1474 and thus it was among the most dominant places.
Ruins of Zalavár
But after the first attack of the Turks in 1532 the population dramatically decreased and the town lost its former significance. As of 1565 the castle operated as a royal border fortress. After the fall of Nagykanizsa in 1600 its importance strongly increased, but in the meantime the settlement and the monastery had become totally uninhabited several times. Service was hard in the castle located closest to the Turks’ military center, Kanizsa. It suffered serious damages in 1644, 1650 and 1682 but otherwise it flanged back many attacks. After the reconquest of Kanizsa in 1690, Zalavár protective functions ceased and the castle was demolished in 1702.
At the beginning of the 18th century the settlement was revived with its former market-town rights but the owner of the monastery and thus the town, the Monastery of Götweig exercised an increasing influence here. So by the end of the century it was included in the surveys as a village only. However, it can be said that the residents of Zalavár lived in a good financial situation, since the marshy fields along the Zala River ensured rich crop yield. Thus the population of the settlement increased at a large pace. Consequently, by the 19th century the majority of the population was cottar, among whom many found seasonal work at the manors in the neighborhood of Keszthely.
In the 1860s, the abbey started several ventures. First it began to exploit a coal site but gave up this plan. Then by 1865, Zala River was regulated so fields that had been marshy earlier could be involved in agriculture.
Agriculture meant a safe living for the residents of the settlement even in the 20th century. The size of arable land was largely increased to the detriment of Kis-Balaton. But by revitalizing Kis-Balaton in the 1990s, the settlement lost a considerable part of its producing land, thereby forcing economic changes that had already been necessary. Since then, the rate of services has strongly risen in Zalavár and tourism has also appeared at the settlement.