What civilisation invented the arch?

This sums up very nicely the generally accepted knowledge:

Arches were used by the Persian, Harappan, Egyptian, Babylonian, Greek and Assyrian civilizations for underground structures such as drains and vaults, but the ancient Romans were the first to use them widely above ground although it is thought that Romans learned it from the Etruscans.

https://en.wikipedia.org/wiki/Arch

The Etruscans were the first civilization to use an arch. The uses of the arch were limited because the arch did not fit in well with the classical architecture. They used the arch when building: gates, bridges and drains.

As a point of interest, you should know that after the Romans conquered the Etruscans, they assimilated the arch to fit into their architectural scheme. It was not a Roman "invention"!

http://www.richeast.org/htwm/Greeks/Romans/arch/arch.html

Only with the Etruscans did the arch reach the formal importance, besides that structural, that this example puts in light.

https://en.wikipedia.org/wiki/Etruscan_Arch

Arch – invented by Sumerians, perfected by Romans.

https://www.reference.com/history/invented-arch-117a7b217728c534