Which pre-Roman Italian civilization taught Rome the arch?

The Etruscans held Tuscany, western Umbria and northern Lazio from around 900 BC, and Rome spent its first couple of centuries as a junior neighbour - three of its seven legendary kings were Etruscan. Almost everything that looks distinctively Roman turns out to have come up the road from Etruria first.

The arch and the vault are the obvious inheritance, though neither was an Etruscan invention; they were the ones who used them at scale in Italy and passed them on, along with the drainage engineering that produced the Cloaca Maxima and drained the marsh the Forum was built on. Also the fasces, the bundled rods that signified authority. Also, less comfortably, the funeral games that grew into gladiatorial combat. Also the alphabet: the Etruscans took a Greek one, adapted it, and handed on the version that became Latin and therefore these letters.

Their religion ran on reading the will of the gods out of physical objects, particularly the livers of sacrificed sheep. A bronze model liver found near Piacenza is marked out into regions inscribed with the names of the deities responsible for each - a working diagram for a discipline the Romans took seriously enough to keep Etruscan specialists on the payroll for centuries.

What we cannot do is read them properly. The alphabet is ours, so anyone can sound out an Etruscan inscription; the language underneath is not Indo-European and is only partly understood, and almost everything surviving is short and funerary. The longest text we have was found wrapping an Egyptian mummy in Zagreb - a linen book cut into strips and reused as bandages by someone with no interest in what it said.