In the neighbourhood are a cromlech and two ruined towers, and crannogs, or ancient stockaded islands, have been discovered in the lough.
Late in the same year or early in 1615 a stockaded trading post called Fort Nassau was erected on Castle Island, now within the limits of Albany, and a few huts were erected about this time or earlier on the southern extremity of Manhattan Island; but no effort at colonization was as yet made.
As a rule they have been constructed on islets or shallows in the lochs, which have been adapted for occupation, and fortified by single or double lines of stockaded defences drawn round the margin.
In rare instances the body of the work is entirely of stones, the stockaded defence and the huts within its enclosure being the only parts constructed of timber.
Warned by the failures of the English against Danish entrenched camps, he introduced the long-neglected art of fortification, and built many burhs stockaded fortresses on mounds by the waterside wherein dwelt permanent garrisons of military settlers.