Learn Finnish: Suuri pylväs lienee pystytetty aukiolle. - The large column was likely erected in the square.

This is the potential mood passive perfect. It combines lienee (the potential form of the auxiliary verb olla, meaning 'is probably') with pystytetty (the passive past participle of pystyttää, 'to erect'). Together, they express that a completed action was probably done to something by an unspecified person: 'has probably been erected' or 'was likely erected'.

Why does the sentence use the allative case aukiolle ('onto the square') instead of a static case for 'in the square'?

In Finnish, verbs of placing, building, or leaving something (like pystyttää, jättää, rakentaa) require a directional case. They focus on the movement of the object toward its final location. Because an aukio (square or plaza) is an open space, it takes external cases. So, the column is erected onto the square (aukiolle), rather than statically in it.

Why is suuri pylväs in the nominative case if it is the object being erected?

In Finnish passive sentences, a total object (an object that undergoes the action completely) is put into the nominative case rather than the genitive-like accusative case. Since the column is a countable whole noun being completely erected, it takes the basic nominative form suuri pylväs.

What is the root of the verb behind pystytetty?