Lang Liêu, the 18th son of King Hùng, had lost his mother at an early age and was left to live a solitary life, tending to the fields and gardens to grow rice and sweet potatoes to sustain himself. While his brothers ventured into the forests and seas in search of rare delicacies, Lang Liêu was saddened and troubled, as his poverty left him with no idea where to find such offerings for the ceremony.
One night, Lang Liêu fell asleep and dreamed that a deity appeared before him. The deity told Lang Liêu to use the products he had cultivated to make cakes—one in the shape of a square and the other in the shape of a circle. The outer layer would be made of sticky rice, with a filling of meat, fat, and onions.
On the day of the Tiên Vương festival, the princes presented an array of exquisite delicacies, rare treasures that only kings could enjoy. King Hùng sampled all the dishes, but when he reached Lang Liêu's offerings, he noticed something unusual. He picked up each cake, contemplated for a moment, and then shared a piece with each of the courtiers to taste. Everyone praised them as delicious. The king remarked, "Lang Liêu's round cake represents Heaven, while the square cake symbolizes Earth. The meat, fat, and onions are the products of Heaven and Earth. The leaves wrapping them signify love and care. Lang Liêu truly deserves to inherit the throne.
King Hùng named these two types of cakes Bánh Chưng and Bánh Giầy. Since then, every Lunar New Year, the people have made Bánh Chưng and Bánh Giầy as offerings to their ancestors and to Heaven and Earth.