In the absence of any Roman occupation, Sweden’s Iron Age is reckoned up to the introduction of stone architecture and monastic orders about 1100. Much of the period is proto-historical, that is, there are written sources but most are of low credibility. The scraps of written matter are either much later than the period in question, written in distant areas, or, while local and coeval, extremely brief. The climate took a turn for the worse, forcing farmers to keep cattle indoors over the winters, leading to an annual build-up of manure that could now for the first time be used systematically for soil improvement.