The Beyeren Armorial, also known as the Armorial of Cornelis van Aeken, was compiled by Claes Heynenzoon (also known as the Gelre Herald, circa 1345−1414), who was Ruwieren King of Arms, the chief herald of the Netherlands, around 1400. Heraldry had steadily increased in importance throughout the Middle Ages. In tournaments and on the battlefield, knights were unrecognizable once they donned their helmet and armor, unless they used a coat of arms as an identifying symbol. The coats of arms also were used to indicate the noble lord to whom the knight had sworn fealty. The herald kept track of the coats of arms and introduced the knights at tournaments, so a solid grasp on international knighthood was essential to his work. Heynenzoon completed the work on June 23, 1405, as stated in the postscript: Explicit iste liber per manus Beyeren quondam Gelre armorum regis de Ruris (Here endeth this book by the hand of Bavaria, formerly Guelders, Ruwieren King of Arms [in the year of our Lord one thousand four hundred and five on the day before Saint John the Baptist’s Day].) Heynenzoon refers to himself as “Bavaria” and notes that he was previously known as “Guelders,” a reference to his role as the herald to the court of the Duke of Guelders. Heynenzoon had previously written the Wapenboek Gelre, or Guelders Armorial, in the late 14th century (now in the Royal Library of Belgium in Brussels, ms. 15652-56). After transferring to the court of Albert I, Duke of Bavaria and regent over the county of Holland, he compiled the Beyeren Armorial while at the court of Holland. The book contains 1,096 colored drawings, mainly grouped in five series showing the coats of arms of: (1) 337 competitors in a tournament at Compiègne in February 1238 (the indicated date may be an error, perhaps intended to be 1278); (2) 191 competitors in a tournament in Mons in 1310; (3) 404 combatants in a foray against the Frisians in Kuinre in 1396; (4) 122 combatants in the siege of Gorinchem in 1402; and (5) 14 sets of “three bests” (the three best Jans, Williams, Adolfs, Dirks, and so forth). Heynenzoon personally compiled the coats of arms from the combatants at the siege of Gorinchem; he derived the others from different sources. The text corresponds to a copy of the armorial dating to about 1500 (Vienna, National Library of Austria, ms. Palatinus 3297, fol. 30): Explicit iste liber per manus beyeren quondam gelre armorum regis de Ruris anno Domini M CCCC V, in profesto sancti Johannis Baptiste.The Beyeren Armorial was incorrectly bound in 1581. In this digital presentation, its original sequence has been restored: folios 1−8, 18−35, 49−57, 36−48, 9−17, and 58−65.