The consecration of the Church of the Three Kings on July 23, 1340 is considered the origin of the Main Festival. From this, Main fishermen and boatmen derived their fishermen's festival, with which they paid homage to "their river and its gifts". They celebrated with "ox on the spit", let wine flow from the fountain of justice and enjoyed passion plays performed by schoolchildren in "Himmelreich huts", goose plucking, duck catching by the fishermen, firecracker shooting, fireworks, and colorful processions in fours and sixes along the banks of the Main.
On the occasion of the inauguration of the new "Old Bridge", the old Main festivals were remembered and an annual folk festival was again held on the Main. Interrupted by the destruction of the 2nd World War, the then Lord Mayor Dr. Walter Kolb continued the tradition. Construction work necessitated a brief move of the Mainfest to the Ostpark, but when it returned from its exile there to Römerberg and the banks of the Main in 1973, the Mainfest was able to celebrate a sensational comeback.