Prothean Beacon

Beacons are ancient Prothean technology. Specifically, they carry the ancient memories of the Prothean civilization as a whole - as well as the secrets of how it vanished. Beacons are set up so only Prothean minds can correctly use and understand their information, which is why Saren and Commander Shepard are desperate to find the Cipher, which will enable them to see the world as a Prothean.

There are two beacons in the Mass Effect universe that have been revealed to us: one on Eden Prime and one on Virmire.