On a small island in Lyckefjärden at Hammarglo in the parish of Mönsterås, lay a fortified manor house. On this islet, a nobleman built a dwelling with a stone cellar for himself and his family. Food as well as taxes from the tenant farmers may have been stored in the cellar. On the islet, houses were also built for the servants and craftsmen and sheds for the cattle. The manor house was strategically placed; it lay on the fairway of the Kalmar straits. It was also easy to defend. The bridge which connected the manor with the main-land has been dated to 1349.
We do not know who may have built the manor house on the islet. At the beginning and middle of the 14th century, the aristocracy gained more power and many noblemen would fortify their manors or erect strongholds. This might have been the case at Källarholmen. The manor may have been part of the Kråkerum estate where Nils Turesson Bielke lived around 1350 and where Israel Birgersson had commitments as well. It is possible that the District Court met on a number of occasions on these islands. Judges from Småland as well as from Östergötland may have gathered here. The location was at this time called Gloholmarna. May even preparations and discussions concerning the new common country-law which was completed in the middle of the 14th century, have taken place on the islet? If so, many noblemen and princes with their escort have crossed this bridge. Nils Turesson Bielke and Israel Birgersson were both close to King Magnus Eriksson.
At an archaeological dig at Källarholmen, one has found pottery, a knife, a whet-stone, and lots of nails for the houses.