Those arms were granted in 1819 and confirmed on 6 February 1841. The oldest known seals of Aalst (13th–14th centuries) show a knight holding a sword in one hand and the Flemish banner in the other, but there is a seal dated 1237 showing the banner with the sword, and even an older seal, dated 1174, with the same features. A later version of the seal (1339–1559) shows a local banner with the sword. A seal from 1407 adds a small shield with the Flemish arms.