The Landgraviate of Hesse (German: Landgrafschaft Hessen) was a principality of the Holy Roman Empire. It existed as a single entity from 1264 to 1567, when it was divided between the sons of Philip I, Landgrave of Hesse.
In the early Middle Ages the territory of Hessengau, named after the Germanic Chatti tribes, formed the northern part of the German stem duchy of Franconia, along with the adjacent Lahngau. Upon the extinction of the ducal Conradines, these Rhenish Franconian counties were gradually acquired by Landgrave Louis I of Thuringia and his successors.
After the War of the Thuringian Succession upon the death of Landgrave Henry Raspe in 1247, his niece Duchess Sophia of Brabant secured the Hessian possessions for her minor son Henry the Child. In 1246 he became the first Landgrave of Hesse and the founder of the House of Hesse. The remaining Thuringian landgraviate fell to the Wettin's Henry III, Margrave of Meissen. Henry I of Hesse was raised to the status of prince by King Adolf of Germany in 1292.
From 1308 to 1311, and again from 1458, the landgraviate was divided into Upper Hesse and Lower Hesse. Hesse was re-unified under Landgrave William II in 1500. The Landgraviate rose to primary importance under his son Philip I, also called Philip the Magnanimous, who embraced Protestantism following the 1526 Synod of Homberg and then took steps to create a protective alliance of Protestant princes and powers against the Catholic emperor Charles V. When Philip I died in 1567, Hesse was divided between his sons from his first marriage, which decisively enfeebled its importance.
The new Hessian territories were: