Harry Themal has it covered at the Wilmington News-Journal. Here is a taste of his article:
No maps exist of the exact location of the fort, except it was obviously near the Rocks, where the expedition commanded by Dutchman Peter Minuit, ended its voyage from Sweden on March 29, 1638.
Dr. Amandus Johnson, whose 1911 two-volume “The Swedish Settlements on the Delaware” is the definitive history, says the fort was completed in May 1638, two miles from the mouth of the Christina where “nature provided a wharf of stone.”
“The fort was built in the form of a square, with [four] sharp arrow-like corners, three of which were mounted with artillery. It was built with palisades and earth and was considered to be strong enough to withstand the attach of a very large number of Indians.”
For that description we must credit Peter Martensson Lindestrom, an engineer who came to New Sweden in 1653 and left when the Dutch took over the settlement. In 1654 he drew maps of the site and the fort along Minquas Kill (the river named for the Minquas Indians), who had established a settlement there. His important drawing was published in his book on American geography and is the frontispiece of Johnson’s book. Minquas Kill is the Christina River.
An original sketch of the fort also once existed, drawn by Minuit and accompanying his log, deed and treaty with the Lenape Indians, but all disappeared en route to an official of the West India Company.