Bernard of Clairvaux preaches his famous sermon in a field at Vézelay, urging the necessity of a Second Crusade. Louis VII is present, and joins the Crusade.

Bernard of Clairvaux, O.Cist., venerated as Saint Bernard, was an abbot, mystic, co-founder of the Knights Templar, and a major leader in the reform of the Benedictines through the nascent Cistercian Order.

Vézelay is a commune in the department of Yonne in the north-central French region of Bourgogne-Franche-Comté. It is a defensible hill town famous for Vézelay Abbey. The town and its 11th-century Romanesque Basilica of St Magdalene are designated UNESCO World Heritage Sites.

The Second Crusade (1147–1149) was the second major crusade launched from Europe. The Second Crusade was started in response to the fall of the County of Edessa in 1144 to the forces of Zengi. The county had been founded during the First Crusade (1096–1099) by the future King Baldwin I of Jerusalem in 1098. While it was the first Crusader state to be founded, it was also the first to fall.

Louis VII, called the Younger or the Young to differentiate him from his father Louis VI, was King of France from 1137 to 1180. His first marriage was to Duchess Eleanor of Aquitaine, one of the wealthiest and most powerful women in western Europe. The marriage temporarily extended the Capetian lands to the Pyrenees.

March 31 is the 90th day of the year in the Gregorian calendar; 275 days remain until the end of the year.