Impersonal verbs

An impersonal verb is a verb that only exists in the 3rd person singular. Its only subject is "it".

Weather
Verbs relating to weather are impersonal.
 * Numquam ningit in hāc urbe. - It never snows in this city.
 * Cur pluit aestate? - Why is it raining in the summer?

Passive verbs of traveling
Verbs of traveling (such as go or come) have passive forms in the 3rd person singular only. The perfect, pluperfect, and future perfect passive forms only use a neuter participle. This is normally used with the action of a group or a crowd.

You might see a passive verb of traveling with a dative or ablative of agent. In this case, translate the sentence so that the dative/ablative of agent is a subject and the verb is active:
 * Ibitur ad Britanniam ab exercitū. - The army will go to Britain. (lit. It will be gone to Britain by the army.)

Sometimes, there is no dative or ablative of agent, but the doer of the action is understood:
 * Venatorēs video. Ventum est per silvam. - I see the hunters. They have come through the forest. (lit. it has been come through the forest.)

Sometimes, there is no doer understood at all. In this case, just supply "one" or "some" as the subject.
 * Non clarum est quō modō eatur ad Romam. - It is not clear how one goes to Rome. (lit. it is not clear how it is gone to Rome)