fortification chain. Other sites probably connected to the Saxon Shore system are the sunken fort at Skegness, and the remains of possible signal stations at Thornham in Norfolk, Corton in Suffolk and Hadleigh in Essex. Further north on the coast, the precautions took the form of central depots at Lindum (Lincoln) and Malton with roads radiating to coastal signal stations. When an alert was relayed to the base, troops could be dispatched along the road. Further up the coast in North Yorkshire, a series of coastal watchtowers (at Huntcliff, Filey, Ravenscar, Goldsborough, and Scarborough) was constructed, linking the southern defences to the northern military zone of the Wall. Similar coastal fortifications are also found in Wales, at Cardiff and Caer Gybi. The only fort in this style in the northern military zone is Lancaster, Lancashire, built sometime in the mid-late 3rd century replacing an earlier fort and extramural community, which may reflect the extent of coastal protection on the north-west coast from invading tribes from Ireland. In Gaul The Notitia also includes two separate commands for the northern coast of Gaul, both of which belonged to the Saxon Shore system. However, when the list was compiled, in , Britain had been abandoned by Roman forces. The first command controlled the shores of the province Belgica Secunda (roughly between the estuaries of the Scheldt and the Somme), under the dux Belgicae Secundae with headquarters at Portus Aepatiaci: Marcae (unidentified location near Calais, possibly Marquise or Marck), garrisoned by the Equites Dalmatae. In the Notitia, together with Grannona, it is the only site on the Gallic shore to be explicitly referred to as lying in litore Saxonico. Locus Quartensis sive Hornensis (probably at the mouth of the Somme), the port of the classis Sambrica ("Fleet of the Somme") Portus Aepatiaci (possibly Étaples), garrisoned by the milites Nervii. Although not mentioned in the Notitia, the port of Gesoriacum or Bononia (Boulogne-sur-Mer), which until 296 was the main base of the Classis Britannica, would also have come under the dux Belgicae Secundae. To this group also belongs the Roman fort at Oudenburg. Further west, under the dux tractus Armoricani et Nervicani, were mainly the coasts of Armorica, nowadays Normandy and Brittany. The Notitia lists the following sites: Grannona (disputed location, either at the mouths of the Seine or at Port-en-Bessin), the seat of the dux, garrisoned by the cohors prima nova Armoricana. In the