Battle of Soissons: King Robert I of France is killed and King Charles the Simple is arrested by the supporters of Duke Rudolph of Burgundy.

The Battle of Soissons was fought on 15 June 923 between an alliance of Frankish insurgent nobles led by Robert I, elected king in an assembly the year prior, and an army composed of Lotharingians, Normans, and Carolingian forces under King Charles III's command. The battle took place at Soissons, near Aisne. Robert was killed, but his army won the war. Charles was imprisoned by Herbert II of Vermandois and held captive until his death in 929. Rudolph, Duke of Burgundy, Robert's son-in-law, succeeded him as ruler of West Francia.

Robert I was the elected King of West Francia from 922 to 923. Before his election to the throne he was Count of Poitiers, Count of Paris and Marquis of Neustria and Orléans. He succeeded the overthrown Carolingian king Charles the Simple, who in 898 had succeeded Robert's brother, king Odo.

Charles III, called the Simple or the Straightforward, was the king of West Francia from 898 until 922 and the king of Lotharingia from 911 until 919–923. He was a member of the Carolingian dynasty.

Rudolph, sometimes called Ralph, was the king of West Francia (France) from 923 until his death in 936. He was elected to succeed his father-in-law, Robert I, and spent much of his reign defending his realm from Viking raids.

June 15 is the 166th day of the year in the Gregorian calendar; 199 days remain until the end of the year.