For threshing with the help of a horse
The long barn was built for threshing* with a threshing trolley, pulled back and forth by a horse. A long barn could be over 40 metres long. The drawback was that the horse had to be unhitched and re-hitched every time it reached the end of the threshing track. The long barn at Hägnan comes from Roknäs village and was built in the 1790s.
This type of long barn became common in Norrbotten in the mid 18th Century, when more effective methods eliminated the hard work of threshing with flails.
*Threshing involves separating the core of the grain from the chaff, the casing that surrounds it.