From Halopedia, the Halo wiki
Daedalus was a deep crater and it's settlement had low sitting buildings, putting them below the rim of the crater. This was not a normal design for settlements on Luna.
During The Reclamation, the EMPs across Earth knocked out power to the settlement in the crater. Roughly two days later, Created Armigers attacked the facility. A few hours later, a partially formed version of Alpha-Nine arrived at the crater to retrieve Vergil from the settlement. They were successful and left soon after with him and Sadie Endesha.
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