Bardaginn byrjar úti.

In Icelandic, the definite article is usually attached to the end of the noun instead of being written as a separate word. So bardaginn means the battle.

This is very common in Icelandic:

• bardagi = battle
• bardaginn = the battle

Here, bardaginn is in the nominative case because it is the subject of the sentence: it is the thing that begins.

A useful comparison:

• Bardaginn byrjar úti. = the battle is the subject
• Ég sé bardagann. = bardagann is an object, so the form changes

So case matters in Icelandic, and the noun form changes depending on its role in the sentence.

Byrjar is the present tense, 3rd person singular form of the verb byrja (to begin / to start).

It is 3rd person singular because the subject, bardaginn, is singular: the battle.

Very roughly:

• að byrja = to begin
• ég byrja = I begin
• hann / hún / það byrjar = he / she / it begins

In this sentence, bardaginn takes the same verb form as it would in English: it begins.

It is an adverb. It describes where the action happens: the beginning happens outside / outdoors.

It is not describing the noun bardaginn directly, so it is not an adjective. If it were an adjective, it would have to agree with the noun in gender, number, and case. Úti does not do that here; it simply gives location.

This is a very common and important distinction.

• úti usually means outside / outdoors as a location
• út usually means out in the sense of movement outward

So:

• Bardaginn byrjar úti. = The battle begins outside
• Hann fer út. = He goes out

A simple way to remember it:

• úti = being outside
• út = going out

Yes, but with rules. The neutral order here is:

Bardaginn + byrjar + úti
subject + verb + adverb

Icelandic main clauses usually follow a verb-second pattern, so you can move another element to the front for emphasis, but the finite verb normally stays in the second position.

For example:

• Bardaginn byrjar úti. = neutral
• Úti byrjar bardaginn. = more emphasis on outside

But Úti bardaginn byrjar would not be the normal main-clause order.

So the word order is flexible, but not completely free.