Learn Polish: Ośmiu żołnierzy wróciło z wojny. - Eight soldiers came back from the war.

When a sentence's subject is a masculine personal number like ośmiu, Polish grammar treats the quantity itself as the grammatical subject. This forces the past tense verb into the default third-person neuter singular form (wróciło) rather than a plural masculine personal form.

Why do we use ośmiu instead of osiem?

The word żołnierzy (soldiers) refers to a group of men, which makes it a masculine personal noun. The standard number osiem is only used for objects, animals, or groups of women. For groups of people that include at least one man, you must use the special masculine personal form ośmiu.

Why is żołnierzy in the genitive case here?

In Polish, any number from five upwards forces the noun following it into the genitive plural case. Because of this rule, the sentence structure is literally closer to 'Eight of soldiers returned.'

Is it possible to use a plural verb for this sentence instead?

Yes, but you would have to change the entire subject phrase. You could say Ośmi żołnierze wrócili z wojny, using the nominative masculine personal number ośmi, the nominative plural noun żołnierze, and the plural verb wrócili. However, the construction used in this example (ośmiu + genitive noun + neuter singular verb) is much more common and sounds more natural in everyday Polish.