Rajhenburg in the older literature used to be mentioned as the oldest castle witnessed in documents in Styria. Document, in which the castle is mentioned as Reichenburch dates to 27^th September 895 when king Arnulf donated in total ownership three kings farms next to Sava at Rajhenburg to his liegeman Valtun, was falsified later. Archdiocese of Salzburg didn't gain the ownership of the former territory of countess Hema Breško-Seliška until the 11^th century (claims, Kos, 2005). Those who oppose this opinion claim that it was only a transcript of older original document which is also supposedly preserved. The research is still in progress.
At the time of Hungarian invasions into the valley of river Sava the castle was destroyed so Konrad I., archbishop of Salzburg, had several castles, among them also Rajhenburg, rebuild in the first third of the 12^th century (Richenburch a novo edificavit). After consolidation after 1131 he had perhaps humble fort superstructured to a castle and populate it with ministerials. In 1141 the first known knight from Rajhenburg is mentioned, Otto de Richenbvrc and the castle is later many times mentiones as a fortress, for ex. in 1309 as castellum Reichenburch and in 1439 as vest Reychenburch in land Steyermark. In 1480 Friderik III. ordered his army to seize all estates belonging to archdiocese in Carinthia and Styria because he did not agree with election of new archbishop Bernard Rohr. Bernard asked for help with protecting the estates of Matija Korvin. In 1491 the truce was made in Bratislava and the castles remained in emperors posession. After death of Friderik III. in 1493 the archbishop at the time, Friderik V., got castles Sevnica and Rajhenburg back from emperor Maksimiljan but had to pay 18600 florints. Again the knights of Rajhenburg ruled the castle. So in 1523 Jurij of Rajhenburg rented sloss Reichenburg with appurtenant estates on both sides of Sava and the right of blood court.
In 1570 knights of Rajhenburg died out.Their heirs became Welzers who also took over old coat of arms of Rajhenburg. It was probably before 1600 when the castle went into the hands of Galla noble Gallenstein. Among various managers we find the following owners: in 1693 Vid Jakob baron noble Moscon, Leopold baron noble Curti, in 1696 count Hanibal Heister, between 1721 and 1802 counts Attems, until 1820 Alojz noble Mandelstein, until 1855 family Delena, followed by Sidonija Brzowska, between 1857 and 1874 count Eberhard Waldburg, between 1874 and 1881 Kristjan baron noble Esebeck, afterwards C. Girand and from 1884 on Trappist monks who rearranged the castle into a monastery. They remained the owners until the last war. At the war time it was a gathering centre for Slovenian exiles and a prison for women after the war. After 1968 the castle is turning into a museum. Today we can find the following exhibitions on the castle: exhibition about the history of the castle and the place named Brestanica over the time, exhibition about Trappist monks, exhibition about Slovenian exiles and exhibition about political prisoners and internes.

French monks - Trappists, the order of reformed Cisterians, the order which commanded very strict rules of monk life, total silence and a principle that anything you need for your life, do it yourself. Monks who populated the castle in 1881 directed the estate mainly into utilitary direction, because they had very developed agriculture, viticulture, fruit growing, they made cheese and castle's meierhof was used and added it the units for manufacturing chocolate Imperial and famous liqueur. The building of a chocolate factory is still preserved and is accessible by passing the cemetary to which once a tree avenue was leading, which does not exist anymore. In 1947 the Trappist order was abolished. By their doing Trappists erased the traces of ancient history by that much, that are only being discovered by systematic architecture-historian research.

Small tower which appears on before- and between- the war photos was a bell tower which was on the roof of the northern wing built by Trappists when they populated the castle. When at the time of World War II the aggressor forcibly removed monks from the castle, the tower was removed soon after that.
Attentive observer will notice thet a tower on a photo is very similar to the tower on Turn under the castle on Vischer's depiction.