Sigtuna was founded on what was then the shore of Lake M�laren just over 1,000 years ago. It took its name from an ancient royal estate (see Uppsala �d) several kilometers to the west (see Fornsigtuna). Various sources claim King Eric the Victorious as founder while others claim King Olof Sk�tkonung.
It operated as a royal and commercial centre for some 250 years, and was one of the most important cities of Sweden. During a brief period at the end of the 10th and beginning of the 11th century, Sweden's first coins were minted here. The old church built in the 13th century by the Dominican order at the monastery still remains, and has had few restorations. The Dominican monastery played an important role in the Swedish Middle Ages and produced many important Church officials. Among them, many Swedish archbishops. Many church and monastery ruins still stand, and the old city structure has not been remodeled, as happened in many Swedish cities during the 19th and 20th centuries.
In 1187 Sigtuna was attacked by Estonian vikings. According to the archaeologist Sten Tesch, excavations have not verified the traditions of destruction of the town. Sigtuna grew and prospered, but around the year 1300 it was surpassed in significance by Stockholm and Uppsala, and remained as a small town.
The current coat of arms can be traced to the city's first known seal, dating from 1311. According to a legend (possibly inspired by the city arms) Sigtuna was once the Royal seat, but this can not be confirmed. The crown may also symbolize the large royal mint which was located in the city. The coat of arms is since 1971 valid for the much larger Sigtuna Municipality.
In the late 19th century, it still only hosted about 600 people, and was the smallest city in Sweden. The city remained insignificant until the second half of the 20th century. Much of the population growth can be related to Arlanda Airport, situated some 10 km from Sigtuna
