One of the peculiarities of the Eastern Baltic region during prehistory is the large number of hillforts. Although their usage dates from around 1200 BC to about 1350 AD, there are several points during this period when notable changes in the functions and fortification types occur. One such point is the 11th century AD. The overall tendency is that in the mid-11th century the overall number of hillforts decreases, but those that remain are built larger and stronger. This paper will present the authors work in creating a detailed and reliable database of hillforts in Latvia, thus enabling analyses of hillfort dynamics in Eastern Latvia (the historical regions of Vidzeme and Latgale) during the 11th century. By analysing the changes, they will be compared with the processes observed in neighbouring regions and the possible reasons for these changes will be sought.