[[Image:|260px]] Cluster View SystemsN/A RelaysN/A Location: Milky Way / Petra Nebula Prerequisite: Priority: Palaven (Mass Effect 3) Note: After completing Priority: The Citadel II, the Petra Nebula becomes inaccessible. The Petra Nebula appears to have been named after the archaeological city in what is now Jordan. Many locations in this cluster, with the notable exception of Elysium, also appear to have been named after places from this region.