11th - 12th century
In the eleventh century the sea came back: this third transgression of Dunkirk was not so bad as the previous one, but the whole region up to Diksmuide was flooded again. Logically, the population searches for refuge on the parts being higher and we may assume that Zandhoofd, that never swamped, was attracting more and more people.
Now silting up and diking go much faster than in the past, largely under stimulation of the abbeys (Dune abbey 1107).
New villages are founded: Oostduinkerke (1080), Ramskapelle (1120)…
The long dune island is getting larger and larger by alluvial soil. Saltings, ideal for sheep breeding, are bordering and finally the name of Zandhoofd is nestled in history.
1085 Abbot Ingelbrecht of the St.-Winnoksabbey in Bergues exchanges with Robrecht de Fries a villa (!) situated on Sandashovad.
1108 Earl Robrecht gives a piece of salting, with the name of Sandashovad, to the abbey of Broekburg.
1120 A bull of Pope Calixtus II mentions Sandeshove.
1183 The inhabitants of Sandeshoven (although already officially renamed on the name of Nieuwpoort)
address a letter to Pope Lucius III.
Some more years (a.o. in 1274 and in 1365) the two names: Sandeshove and Nieuwpoort are still mixed up. But the melodious and much older Sandeshove was inferior to Novus Portus or Nieuwpoort.
Not only Nieuwpoort and Sandeshove are identified with each other still for a long time. In 1150 Isera Portus is still mentioned and in 1163 there is some talk of Neoportus and Novum Oppidum. Nevertheless Novus Portus (Nieuwpoort) is used more and more and finally gets the upper hand.
Why this rename? In 1150 Isera Portus had already extended to a settlement, which meanwhile was more important that Lombardsijde, a town. To make matters worse for the people of Lombardsijde, the northern arm of the IJzer silted up more and more, and a more suitable location for a port had to be found. Philip of the Alsace did the most obvious thing: he created a completely new city, taking in the older Zandhoofd, systematically parcelled in straight streets, with walls around and reinforcements. In order to make his support real, he gave a charter, with rights and freedoms, to the new port and town, and finally a new name which was determined forever: 1163: NOVUS PORTUS.