Nobleman Owain Glyndwr was born circa 1359 into a prosperous family in north Wales, studied law in London and was a loyal veteran of service to King Richard II of England. But in 1399 Henry Bolingbroke, exiled heir to the Duchy of Lancaster, deposed his cousin Richard and had himself declared King Henry IV. Reginald de Grey, 3rd Baron Grey de Ruthin—a member of the king’s council and confidante of Henry—took advantage of his position to seize a contested portion of Glyndwr’s land. At that Glyndwr led other disaffected Welshmen in revolt.

On Sept. 16, 1400, the rebels proclaimed Glyndwr Tywysog Cymru (Prince of Wales), a title Edward I had expropriated a century earlier for heirs apparent to the English throne. Their selection was in essence a declaration of war. Henry moved to quell the uprising, but the revolt soon spread through north and mid Wales. Glyndwr captured Grey in early 1402 and held him for ransom. That year Parliament instituted a set of laws intended to further subjugate the Welsh, but the acts only drove more rebels to Glyndwr’s cause.

That June 22, in one of the few pitched battles of the revolt, a 2,000-man Anglo-Welsh force under Sir Edmund Mortimer, 5th Earl of March, confronted Glyndwr and 1,500 followers near Pilleth in the lordship of Powys in mid Wales. Just before the clash Glyndwr divided his army, placing his archers in plain view on Bryn Glas (Green Hill) and concealing the rest of his men in flanking woodlands. As the Anglo-Welsh troops advanced uphill, Glyndwr’s Welsh longbowmen outdistanced Mortimer’s archers and exacted a terrible toll, forcing Mortimer to commit his men-at-arms to a charge. At that moment Glyndwr sprang his trap on the English rear and flank, prompting a rout. For the loss of about 200 men, Glyndwr killed some 600 English, including several prominent knights, and captured Mortimer. When Henry refused to ransom Mortimer, Glyndwr persuaded the earl to join his cause. That fall Mortimer married Glyndwr’s daughter Catrin.

As a consequence of the stunning victory at Bryn Glas the Welsh uprising persisted until 1415, the English ultimately regaining control through a combination of force and diplomacy. Glyndwr—who vanished from the record—remains a legendary catalyst of Welsh national identity.

Lessons:

Let your reputation precede you. Early in the campaign foul weather sparked a rumor among the English that their Welsh opponent was a wizard who could control the elements, a myth Glyndwr was perfectly content to encourage.

In an archery contest, gravity is your friend. Only overconfidence can explain Mortimer’s decision to en-gage Welsh bowmen holding the high ground, as elevation offered Glyndwr’s archers a natural advantage in range.

Division can pay great dividends. As Robert E. Lee would discover at Chancellorsville, Va., 461 years later, Glyndwr proved that a divided force, aided by concealment, timing and the element of surprise, could overcome a stronger opponent.

Diplomacy has its place in the art of war. Glyndwr knew the deposed Richard II had named Sir Edmund Mortimer heir apparent to the throne. Once he’d captured Mortimer, the Welshman used that and Henry’s failure to ransom the earl to win over his captive—sealing the deal with Edmund’s marriage to his eldest daughter.