From what I read about the Mass Effect 2 DLC Arrival, Shepard destroyed the Alpha Relay because this was going to be an entry point of the Reaper invasion, so destroying it delayed the invasion.

Even though the Citadel has a mass relay inside it, there is a smaller one in the Widow Nebula which is used to reach Citadel for most beings. And we see that Sovereign uses the external relay without some sort of overload to the relay. (Sovereign and a Geth Armada also used it along with the Alliance Armada).

Why did the Reapers need the Citadel to be a mass relay when they could have just used the nearby one and then block communications to prevent any warning from getting out?


The reapers set up the Citadel so that it would become the center of government for the dominant civilization(s) of each cycle. This would make it simple to remove the top levels of leadership as well as make it easier to disrupt and intercept galactic communications.

As for why it needed to be a mass relay, this gave the reapers a backdoor into the Widow Nebula, allowing the Reapers to bypass the majority of any defenses that may exist between the galactic rim and the Citadel. The Citadel relay only connected to the dark space location where the Reapers hibernated, similar to the Omega-4 relay only connecting to the Collector base near the galactic core. And by building the relay into the Citadel and having the Keepers manage the Citadel, the child races would be kept from discovering it's real purpose.


I agree with @Xantec's answer. But to add to it, keep in mind that near the end of Mass Effect 3,

the Reapers move the Citadel to orbit Earth.

Therefore they probably wanted to make sure that the relay in the Widow Nebula was not exclusively relied upon for travel to the Citadel.

  • Once the Reapers were in the galaxy they hardly needed the relay to be in the nebula anymore. Assuming that they had won, they likely would have moved it back there before retreating back to dark space. – Xantec Jun 12 '14 at 12:42
  • @Xantec I'm confused by your comment. I'm not saying the Citadel has to stay in the nebula. I'm saying if it ever gets moved away from an external relay, it would be safer for the Reapers to make sure the Citadel itself has one so it isn't too hard to get too if someone else moves it before they come. – Mufasa Jun 14 '14 at 1:08

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