In an attempt to put its fur trade on a secure footing, the New Netherland Company in 1614 established “a redoubt or small fort [..] with a small garrison” on the Hudson River. The Fort of Nassau is wide 58 feet square within the walls, the moat is 18 feet wide. [..] The house was 36 feet long and 26 wide in the fort. Even though the accuracy of De Laet’s description is subject to doubt, the reference to “the form of a redoubt,” “walls,” and a “moat of eighteen feet wide” suggest that the outer works of Fort Nassau consisted of earthworks of a simple shape, without protruding points or bastions. There is no reference to a palisade or stockade and while that should not be interpreted as proof of its absence, it makes it unlikely that the perimeter defence of Fort Nassau consisted of a vertical wooden structure, as has been proposed by Len Tantillo. Assuming that the moat (gracht) was filled with water and was not a dry moat or ditch (greppel), a direct connection to the Hudson River is a conceivable option. In that case, it is likely that Fort Nassau was constructed on the bank of the river and that the side facing the river remained exposed, especially if the two cast guns were located in a position that allowed a clear field of fire over the river. The proximity to the river made Fort Nassau vulnerable to flooding. Van Wassenaer does not specify in which year Fort Nassau was abandoned, but Moulton asserted that it happened in 1617, while O’Callaghan preferred 1618 probably on the basis of Stuyvesant’s letter of 1660, referred to below. There is no convincing documentary evidence for either suggestion, even though both years are frequently referred to in popular historiography and on websites.
If the precise chronology of Fort Nassau is uncertain, so is its location. Fort Nassau was constructed on Castle Island (Casteels Eyland) but the exact location is difficult to pinpoint, as the evidence is contradictory. On the 1614 map of New Netherland, a small mark in the middle of the island may indicate its location, but on a later Vingboons map a larger mark can be discerned on the north point of the island. Yet on the ca. 1632 “Gillis van Scheyndel Map” a farmhouse (Welysburg) is located on the north point. These discrepancies are probably due to inaccuracies in cartography as well as to changes in the island’s topography as frequent flooding caused erosion and sedimentation. A flood in April 1640 covered Castle Island with water four feet deep, as the river rose to twelve feet higher than its regular level. The floods that severely damaged Fort Orange in 1647/1648 and 1666 very likely also hit Castle Island.
While remnants of the fort were still discernible in 1680, it is likely that flood erosion gradually removed them. On May 22, 1833, the New York Evening Post carried an article about a devastating flood of what was then called Patroon’s Island. The flood “swept every vestige of vegetation of its surface” and “the entire surface of the soil is washed away to the depth of several feet.” The newspaper reported that “Human skeletons, buried after the Indian manner, in a sitting posture, have been exposed” by the flood, but there is no reference to any remains of Fort Nassau. This omission increases the likeliness that at this point in time, almost 220 years after its construction, few if any traces of Fort Nassau remained.
On the basis of documentary evidence then, it is impossible to locate Fort Nassau with certainty on either the middle section or the north end of Castle Island. This makes it difficult to determine where to start an archaeological investigation, which may not even yield a result. Apart from earlier floods, the 1833 flood, purportedly removing a considerable portion of the topsoil, may also have washed away the sub-surface remainders of the fort, with the possible exceptions of a stone or brick foundation of the dwelling house and the traces of a dugout moat or well. Even if an excavation turned up such traces on Castle Island, it may well be impossible to determine whether they pertain to Fort Nassau from the 1610s or to the farm from the 1630s. In sum, the subsequent development of Westerlo Island, as it was called in the nineteenth century, into an airfield and, later on, the Port of Albany-Rensselaer, as well as the filling in of Island Creek and the construction of a railroad make it unlikely that the exact location of Fort Nassau will ever be established or that remains will be uncovered.