I often read that favourite weapon of a viking were axe. But on what is this based on?
I know that in general axe was second most common weapon on battlefields after spear regardless of nationality.[/list]

The spear was the primary weapon but everyone carried some kind of sidearm. Swords were hideously expensive so what alternative sidearm would you propose? In my mind there are only two options: knife, axe.

But this don't answer my question. Because axe were cheapest side arms then It applies to everyone not only Vikings so why axe suppose to be exactly their favourite weapons?

Axes were common all over the continent. The throwing axe was so prevalent among the Franks that the Spanish called it a "francisca". Gregory of Tours names two different axes: securis and bipennis.

In my contry Poland axe are second most common weapon finds in battlefield some in graves in great moravia one type of ax was very popular both in infantry and cavalry so what is so different with Vikings?

Especially with shieldwall spear is by far the best weapon.
And more sax which were somewhat popular with Vikings, no similar weapon among Slavs so theoretically Vikings have more types of side weapon.

About topic about law. Sorry but laws from 15+ have nothing to with Vikings.

https://myArmoury.com/talk/viewtopic.php?t=32114

Ok so from this topic i got info about Scandinavian laws of 11+ to carry weapons which always consist of shield and spear then axe or sword so expensive or cheap option.

But I don't know such document from France or I don't know any exact archaeology source from batlefields which is the best source.

In Poland nobody say that axe was popular weapon but is just is in archelogical findings, and even more in great moravia where bradatica axe is very common.

I'm not sure we can claim fighting axes to be super popular among vikings. We have found an insane amount of swords in Norway from the viking era, so swords were most certainly common. What we do have, however, is a connection between Norwegian nationalism in the 19th century (when in union with Sweden), fighting axes and Vikings. Vikings were seen as the mythical and glorious ancestors, and since Norway was the last place still using fighting axes in a military context (so, not including axes as tools), Norwegian nationalists figured that vikings had to use a lot of axes. It was simply a question about national pride and identity. I believe a lot of what makes vikings popular today is born from the mythical status they gained then.

Axes in general was a very important part of the Norwegian/west Scandinavian society for a long time. All the way from the Bronze age until the industrialization axes has been important as tools, currency or weapons. In the viking era, and earlier, we exported iron in the form of stylised axes as well as specialized tools. So axes was certainly an important cultural object. But whether it was more common than the sword on the battlefield among Norwegian Vikings, I'm not so certain.

Do note, I am talking primarily about Norway and Norwegian Vikings. It is where I'm from and what I know most about. It is by no means certain it carries over for Swedish, Danish or Icelandic early medieval people.

But even in Poland nobody say that axe was favourite weapon.
In Poland we also have findings of stylesied iron/silver in shape of axe used as form of currency.
And we know of big number of axes from findings in lake lednickie, so its a lot equipment which just fell to water so its much more good example of weapon used in battles.

And about france how we know that they don't use axes?

From Norwegian 13th century law on militias quoted from user Baard H and his post in the following thread:
http://myArmoury.com/talk/viewtopic.32114.html
Already mentioned by Pawel P

"5. But when a working man takes his first service for full wages, then he shall the first summer buy an axe, the second a shield and the third a spear. But if he lacks any of these three weapons, then he shall pay fine to the king of one øre for every one he lacks. But if he lacks them all, then he shall pay fine of one øre to the king and have only half-rights until he get hold of weapons. "

All earlier Norwegian law tend to go something like :bring shield, spear and either sword or axe also one bow per bench (every 2 people) with some difference in weapons and armor depending on the person's wealth. Read the thread linked above for more info.

Swords can be seen the early period as a luxury weapon, as they need more skill, and better metal supply to make.
And they don't really do anything other weapons don't do, a sword is the sports car of the day so to speak.
Where as you basically need a spear and shield to fight in a battle line and a small hand axe/ large knife gives you a back up.