The Casuari were an ancient Germanic people. Ptolemy mentions them as living on the southern border of Germany, east of the Abnoba mountains, that are east of the Rhine. They were therefore neighbours of the Tencteri, a tribe living between the Rhine and the Abnoba mountains. Their origins can be traced back to those of the Alemanni and Khatti, they descend from Assyrian tribes who migrated into Europe to settle. Ptolemy also mentions them as having founded the town of Suevos Casuari. The Casuari were most likely numerous during and around the time of Ptolemy, which is around 90 to 168 AD. Being a small tribe, very little remains of them, and most evidence comes from written sources.
The Casuari spoke a South Germanic dialect, related to the High, or Upper Germanic languages. The location of their tribe was in fact a crossroad between the Weser-Rhine Germanic and Elbe Germanic languages. If so, their language originated from the Rhine, Alps, Elba or the North Sea from Friesland to Jutland.
By the time of the fall of the Western Roman Empire, the Casuari had most probably been conquered by the Romans, or had either become part of the Alemanni or another major Germanic tribe on the Rhine river.