On the top of Mount Hammaren lies 5 stone cairns from the Bronze Age. The biggest of them is perhaps 15 metres long. On the south side of Mount Hammaren is a big gravefield from the Iron age situated. It contains about 150 graves. Graves from both older and younger Iron Age are to be found here. As the younger Iron Age went on the thought was developed that each farm should have their own gravefield instead of, as it had been earlier, that several farms shared one big gravefield. The biggest and most obvious example is called “Fornkullen” and is situated just behind Olberga School. It contains about 70 graves. The first time both Sibble and Olberga was mentioned in the written records was when one knight gave away both of them to the church to save his soul from harm in the afterlife, a very common practice in medieval times. The year was 1342. School became mandatory in Sweden 1842. The result of that was that new schools were needed and in 1866 Olberga School was built. It is still serving as a schoolhouse. It is a low red painted wood building with white gables.