Question: What was the reason for churches being built 1,00 years ago in Norway?
About the article "Norway", section "Architecture".

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The Church of Norway has 21 churches within the municipality of Trondheim.
They are all a part of the Diocese of Nidaros, which is based in Trondheim at the Nidaros Cathedral.
Many of the churches are several hundred years old, with a couple which were built almost 1000 years ago. 
Church building in Norway began when Christianity was established there around the year 1000.
The first buildings may have been post churches erected in the 10th or 11th century, but evidence is inconclusive.
For instance under Urnes stave church and Lom Stave Church there are traces of older post churches.
Post churches were later replaced by the more durable stave churches.
About 1,300 churches were built during the 12th and 13th centuries in what was Norway's first building boom.
A total of about 3,000 churches have been built in Norway, although nearly half of them have perished.
From 1620 systematic records and accounts were kept although sources prior to 1620 are fragmented.
Evidence about early and medieval churches is partly archaeological.
The "long church" is the most common type of church in Norway.
There are about 1620 buildings recognized as churches affiliated with the Church of Norway.
In addition there is a number gospel halls belonging to the lay movement affiliated with the Church of Norway (not regarded as church buildings) as well as churches belonging to other Christian bodies.
Until the 20th century most churches were built from wood.
220 buildings are protected by law, and an additional 765 are listed as valuable cultural heritage. 
The first town formation known in North Norway, "Vågar", was situated around the narrow, natural harbor near Kabelvåg, just west of Svolvær.
Vågar is mentioned in the book Heimskringla, and might have been established as early as the year 800.
One of the first churches in North Norway was most likely built here, approximately 900 years ago.
The great cod fisheries in winter has always been the most important economical foundation for the town, but fish farming (salmon) is also important in Vågan, as is Secora and Lofotkraft. 
Round-tower churches are a type of church found mainly in England, almost solely in East Anglia; of about 185 surviving examples in the country, 124 are in Norfolk, 38 in Suffolk, 6 in Essex, 3 in Sussex and 2 each in Cambridgeshire and Berkshire.
There is evidence of about twenty round-tower churches in Germany, of similar design and construction to those in East Anglia.
Countries with at least one round-tower church include Andorra, the Czech Republic, Denmark, France, Italy, Sweden, Norway, Poland and South Africa.
The distinctive feature of these churches is, of course, their round towers.
The reason for their construction – mostly by the Saxons – is a matter of dispute.
Suggested explanations include the following: Round-tower churches are found in areas lacking normal building stone, and are therefore built of knapped flint.
Corners are difficult to construct in flint, hence the thick, round walls of the towers.
The churches are found in areas subject to raids from, for example, the Vikings, and were built as defensive structures, churches being added later.
In fact, however, the towers are generally too short to have been of much use defensively, and the towers were often added to existing churches, having flat walls where they joined the main structure.
In 937 King Athelstan (924–939), the first King of all England, decrees that a bell tower be built on the land of every thane; an existing trend of building bell towers on to existing churches was thus accelerated.
Many other (less likely) explanations are offered in communities containing the churches, including appeals to ancient stone circles and the remains of wells.
Round-tower churches should not be confused with similarly shaped structures such as the Irish round towers found in Ireland and Scotland, or with round churches, which have a circular plan and are often found in Denmark or Sweden. 
  Wooden Church in Poiana Botizii, built in the 19th century (1825), historic monument  Black Pond Nature Reserve (1,00 ha), natural monument  “Botiza Glade” Bone Cave Nature Reserve (0,50 ha), natural monument