The Chatti (also Catti) were an ancient German tribe settled in central and northern Hesse and southern Lower Saxony, along the upper reaches of the Weser river and the valleys and mountains of the Eder, Fulda and Werra river regions, a district approximately corresponding to Hesse-Cassel, though probably somewhat more extensive.

The Chatti successfully resisted incorporation into the Roman Empire, joining Arminius' coalition of tribes that annihilated Varus' legions in 9 A.D. in the Battle of Teutoburg Forest, and Rome eventually responded to the belligerent defense of their independence by building the limes border fortifications along the southern boundary of their lands in central Hesse during the early years of the 1st century. The remnants of a very large fortified retreat have been found on a hill near the village of Metze (Latin: Mattium) in the core lands of the Chatti south of Kassel.

According to Tacitus in his Germania (book) (chapter 30), they were disciplined warriors famed for their infantry, who (unusually for Germanic tribes) used entrenching tools and carried provisions when at war. Their neighbours to the north were the Usipi and Tencteri .

The Chatti eventually became a branch of the much larger neighboring Franks and were incorporated in the kingdom of Clovis I, probably with the Ripuarians , at the beginning of the 6th century. They are mentioned in the Old English epic Beowulf as Hetwaras.

In 723, the Anglo-Saxon missionary Winfrid -- subsequently called St. Boniface, Apostle of the Germans -- proselytizing among the Chatti, felled their sacred tree, Thor's Oak, near Fritzlar, thereby initiating the conversion of the Chatti and the other German tribes to Christianity.

The Chatti and the Frisians are the only Germanic tribes today still living in the same region they occupied at the time of Christ. "Chatti" eventually became "Hesse" through a series of sound shifts.