Why did viking women wear long dresses?

Firstly, it is very cold in northern Scandanavia! Also, it was socially unacceptable for a woman at that time (other than a prostitute) to show her body off. A married woman also had to have her head covered. Only young, unmarried girls and prostitutes would wear their hair loose and uncovered. If a married woman (or man) was dressed inapproriately this was grounds for divorce in Viking society!

A viking dress or tunic was called a Kirtle. Viking women would wear several layers of clothing - underdress of linen, an overdress of wool or linen and, in early viking period, an apron dress called a hangerok. These would vary in colour and decoration depending on the woman's status.

Hope this helps.