Learn Italian: Bisogna far costruire la parete ai muratori. - It is necessary to have the bricklayers build the wall.

This is the core rule of the causative fare + infinitive construction. When the second verb (costruire) has a direct object (la parete), the person actually doing the action must be introduced by the preposition a. Literally, you are 'making the wall be built to the bricklayers'.

Why is the verb written as far instead of fare?

In Italian, it is very common to drop the final -e of fare when it is immediately followed by another infinitive. This makes the sentence flow more smoothly. You will see this truncation frequently in causative constructions like far costruire.

Why isn't there a subject before bisogna?

Bisogna is an impersonal verb that means 'it is necessary' or 'one must'. It only ever exists in the third-person singular and never takes a personal subject like 'I' or 'you'. It is always followed directly by an infinitive, which here is far.

Why use parete instead of muro for 'wall'?

While both mean 'wall', muro usually refers to an exterior, structural, or heavy brick wall. Parete typically refers to an interior dividing wall inside a room or building. The bricklayers here are likely building a partition wall inside a house.