Two thousand years ago, it was a pilgrimage festival in which they brought the firstfruits of wheat to the Temple, sacrificed and ate lamb or Capricorn. The first mention of the custom is in medieval France, around 1270.
Baladan, according to Rabbi Prof. David Golinkin, is a corruption of feldan, a dairy food, and it is possible that the custom of eating dairy foods developed in France. The basic dairy foods mentioned in the Bible are "butter," which Abraham served with a veal to the angels.