Sandby Borg

(Sandy Borg, from Archaeology Magazine)

It looks like the 5th century was a pretty grim time on the island of Oland, Sweden.  Over the past five years, archaeologists have been excavating the ringfort of Sandy Borg.  Oland is a long, narrow (85x9 miles) island located off the southeast coast of mainland Sweden (see map below, Oland is within Box 1).  This article in Archaeology Magazine provides the most background.

Sandby Borg, one of 15 ringforts known on Oland from the era, covered an area about the size of a football field, within which were 53 houses, surrounded by a rampart 15 feet high.  Although the excavation has uncovered less than 3% of the site, mostly concentrated on a 1500 square foot house, it is clear that a massacre occurred.  Fourteen skeletal remains have already been found, all showing violent deaths, and it is thought that hundreds may have died. The 5th century was a time of endemic warfare on the isle and elsewhere in the region, but archaeologists have discovered several striking aspects about what happened at Sandby which have created an aura of mystery around the site.
(Artist's recreation of Sandby, from Ars Technica)

The first is the discovery of Roman coins, including golds coinage, minted during the reign of the Emperor Valentinian (425-55 AD).  While Roman coins have occasionally been found elsewhere on Oland, Sandby has an unusually high concentration of such findings. Some historians believe the Roman historian Tacitus may have made reference to Oland in his Germania (98AD) but certainly by the 4th century as the northern tribes entered their era of the great migrations, natives from the islands traveled south to serve in the Roman military and as raiders of the empire.  The 5th century coins appear newly minted and unmarked indicating that they were directly given to the men who settled in Oland. This period ended near the end of Valentinian's reign, which is also when the last dated coins are found at Sandby.  With Valentinian's death, the Western Roman Empire, which had been struggling to survive for fifty years, entered its final death throes, becoming, for the most part, a shadowy presence, before it was finally put out of its misery with the deposition of the last emperor in 476. The archaeologists think this ringfort was where most of the returning unemployed Roman mercenaries lived.
(Roman coin found at Sandby, from Ancient Origins)

Then there is the fact that, unlike the other Oland ringforts, Sandby seems to have been occupied only briefly, a few months at most, before its destruction.  The excavations have not shown layers of occupation.  Why the site was built and why it lasted for such a brief time is unknown.

Third, is that there is no evidence of looting which is highly unusual, as that was often the main motive for such attacks.  The inhabitants apparently expected an attack and buried caches of coins and jewelry have been found, all to the left of the doors of the houses, but in addition it does not seem that the attackers took any of the livestock or anything else from the homes.  In fact, the raiders left the livestock penned up, to die of starvation. They came, they killed, they took nothing, and left, which is extremely odd behavior.
(Buried brooch recovered in excavation, from Ancient Origins)

Finally, the people who inhabited the site and the location itself were shunned for some unknown reason.  The site has remained uninhabited and, even more unusual, left untouched, not even looted, since the massacre  and for the entire time since then stories have circulated about the site.  As Ars Technica reported in its article on Sandby Borg:

Even today, people in local villages say they were warned not to visit the ruins as children because of ghosts and curses.

Perhaps, as the excavation continues, we will learn more about who the inhabitants were, why they died and why the site was not looted.  This link takes you to the official website for the excavation.