The ommegang (literally "walk around") was the most grandiose pageant of the year during the late Middle Ages and early modern period. It was born sometime after 1348—its first official mention is 1359—as a ceremonial procession in honor of the Virgin Mary, who purportedly worked a miracle (1348) in assisting an impoverished cloth worker, Beatrice Soetkens, and her husband to secure a statue of her image to grace a chapel in the church of Notre-Dame du Sablon. A great procession wound through the city streets, the statue held aloft. The event soon acquired a more profane character and municipal authorities and leaders of the craft guilds came to play a prominent part. The parade attained a high point in splendor on 2 June 1549 when Emperor Charles V and his son, the future king Philip II, attended. By that date, the entire city population participated. Courtiers, ambassadors, academics, and members of the nobility and military would process accompanied by floats decorated al-legorically to depict virtues such as Hope, Charity, and Joy.
The ommegang fell into decline during the wars of religion and stopped completely in 1580. It was revived by Archduke Albert and Archduchess Isabella in 1615. Its present-day manifestation derives chiefly from the efforts of folklorist Albert Marinus, who won approval from city officials and secured subsidies from well-to-do donors. It was first reprised in 1930 to commemorate the centenary of Belgian independence and the 550th anniversary of the Grand Oath of the Crossbowmen of Saint George, who played a leading role in early pageants. The parade proved costly, lasting six hours and involving hundreds of medieval-costumed characters, floats, and musical bands. It was decided to hold an ommegang once every 10 years, but World War II intervened. After the war, an annual event restricted to the Grand' Place has been held in July. It re-creates the pageantry associated with the ommegang of 1549.
Historical Dictionary of Brussels. Paul F. State.