Electri-City is an ancient city run entirely on electronics, mentioned in the description for Akihabana. This could possibly be the city that the Searchers stumble upon in the anime series when they meet Henger, and probably the city that Monol tells them about where the ancient technology was kept. This may mean that it was built by the Pendant civilization.
The Pendant scientists used a very powerful Shrine in this city to modify the Phoenix for battle with Moo, after escaping the destruction of their own city. It is assumed that while they were there, they evacuated who they could from the city and left the robots in charge of the rest.