Learn Italian: Sebbene avvertiti del pericolo, abbiamo deciso di documentare il luogo. - Even though warned of the danger, we decided to document the place.

This is an implicit concessive clause. You can combine concessive conjunctions like sebbene, benché, or pur directly with a past participle to make the sentence more concise. The past participle essentially functions as an adjective in this structure.

Why does avvertiti end in an -i?

In these implicit clauses, the past participle must agree in gender and number with the subject of the main clause. Since the main verb is abbiamo deciso (we decided), the implied subject is noi, making the participle masculine plural.

If I wanted to use a normal conjugated verb instead of this shorthand, what would it look like?

You would need to use the subjunctive mood, because sebbene requires it when followed by a conjugated verb. The explicit version would be Sebbene fossimo stati avvertiti del pericolo (Even though we had been warned of the danger). The implicit form with just the past participle saves you from having to juggle the past perfect subjunctive!

Why is there a di in abbiamo deciso di documentare?

As a quick refresher from earlier levels, many Italian verbs require a specific preposition before a following infinitive. The verb decidere (to decide) always takes the preposition di when it is followed by another action.