Historical map of the province of Östergötland published in 1779 by Nils Morelius, chief inspector at the Lantmäteriet. The oldest found traces of human existence in Östergötland originate from the Old Stone Age, more than 9,000 years ago, when this part was a bay of Lake Ancylus. The sites from the Early Stone Age (3000 BC) are all located on the fertile plain that stretches south of the Motala stream from the Vättern to the Baltic Sea.
Even during the Bronze Age, the main settlement was in the western part of the landscape, but farming spread increasingly eastwards, as can be seen from the many petroglyphs found at Roxen and in the Norrköping area. Himmelstalund has around 1 660 petroglyphs, which are the second largest in Sweden after Tanum.
During the Iron Age, a large expansion has taken place in the area during the period 0-400 AD. There are 75 settlements, 500-600 graves, another 30 kilometres of stone tracks, about 1000 ancient fields, a road system of about 10 kilometres with at least 14 bridges and a paved road crossing. During the Iron Age, Östergötland's many ancient fortresses were also built, some of which are considered to have been erected to defend against invaders during the Migration Period.
From the same time, a large number of tribes in southern Sweden are mentioned for the first time, including the name ostrogothæ appears in the list written in the 5th century in Italy by the Gothic writer Jordanes, but although many would like to interpret this as Östergötland, the name is associated with other names that only concern western Sweden, so it may seem more likely that it was part of the country in the west. The concept of Västergötland and probably Östergötland is younger.
Source reference: Wikipedia (CC BY-SA)