Templars knights raised their seat in Laon in 1128. In 1134, pope allowed them to raise a chapel dedicated to saint John the Baptist. And when the order was dissolved in 1312, it was Saint-John of Jerusalem order who owned the chapel...
Façades are pretty sobers, with only little heads sculpted on the cornice. We have 3 parts: the rectangular porch, the rotunda and the circular apse: it looks like the octagon of Montmorillon, also raised by the Jerusalem order, based of St-Sepulchre in Jerusalem!