The Tripartite Indenture was an agreement made in February 1405 among Owain Glyndŵr, Edmund Mortimer, and Henry Percy, 1st Earl of Northumberland, agreeing to divide England and Wales up among them at the expense of Henry IV. Glyndŵr was to be given Wales, and a substantial part of the west of England, including the English portions of the Welsh Marches. Northumberland was to have received the north, as well as Northamptonshire, Norfolk, Warwickshire, and Leicestershire. The Mortimers were to have received the rest of southern England.
The three parts met at Onennau Meigion, a point where ash trees called grew (52.496076,-2.318025), between Bridgnorth and Kinver. Onennau is the Welsh term for 'ash trees', and a village called Six Ashes still exists to this day on the Shropshire/Staffordshire border. The agreement defined Glyndwr's part as:
- the whole of Cambria or Wales divided from Leogria now commonly called "England" by the following borders, limits, and bounds: from the Severn estuary as the River Severn flows from the sea as far as the northern gate of the city of Worcester; from that gate directly to the ash trees known in Cambrian or Welsh language as Onennau Meigion which grow on the high road from Bridgnorth to Kinver; then directly along the highway... to the head or source of the River Trent; thence to the head or source of the river commonly known as the Mersey and so along to the sea.