 Katwijk aan Zee and Katwijk aan den Rijn were part of the same heerlijkheid called "Beide de Katwijken en 't Zand" (or something similar).They have been administratively joined for centuries.In 1520 a Roman ruin known as "Brittenburg" emerged from the shifting sands on the beach just south of the mouth of the Oude Rijn, much to everyone's astonishment.