Vikings, an industrious bunch
What jumped out from the video was 'The Viking Museum in Roskilde, Denmark', which was visited 2 years ago. It provides an amazing look into the past 1,000+ years. Most noteworthy, IMHO, is that many of the vessels displayed in the museum were salvaged from the floor of the bay, from a specific area on the floor of the bay. That's when the story gets interesting:
For centuries, fishermen and seamen navigated around a 'bump' in the center of the harbor opening when entering/exiting. The 'bump' had a specific width & length and created a thin water region centered in the harbor opening. It was a feature that was thought to always be there, a 'Mother Nature' anomaly. In the late 50's, early 60's, this assumption was proven false when 'the bump' was found to be formed by the skeletal remains from a stack of Viking ships permanently scuttled to block the entrance and protect Roskilde, at the time the capital of Denmark, probably to keep either the invading Swede's or Norwegian's at bay (literally).
The in-laws we were visiting (yes, it's good to have Danish in-laws!) recalled dates they took to the site in their youth in the mid-60's, on an excursion boat that circled the archeological dig, providing a peek to what lay on the bottom.
Thus ends today's Viking history lesson!