Germanmusical theoristFranco of Cologne publishes Ars Cantus Mensurabilis, in which he advances a new theory of musical notation in which the length of a musical note is denoted by the shape of that note, a system still used today.
May 21 - Kublai sends his envoy Hao Jing to negotiate with Song Dynasty Chancellor Jia Sidao, after the small force left by Kublai south of the Yangzi River is destroyed by a Chinese army of the Southern Song Dynasty. Chancellor Jia Sidao imprisons the entire embassy of Kublai. This slight will not be forgotten by Kublai, but he is unable to assault the Song due to the civil war with his rival brother Ariq Böke.