sentences:  The largest, Vengleuz Braz, was located west from Kermeur.With its cliffs, local water resources, isthmus crossable only at low tide and its location defending Brest harbour, Île Longue is an easily defendable, strategic location.It was fortified by Vauban and Dajot as to render the roadstead impossible to hold by an enemy fleet and to allow a counter-attack against an enemy landing party attempting to seize Quélern.