[SPOILER] Engineer's last speech

[Alardem]

I've seen a couple of other people taking the 'house of skulls' to mean a reference to Aztec sacrifices, which raises the interesting possibility of the Machine/Engineer's long-term view of time. He juxtaposes the carnage brought about through the scientific achievement of the atomic bomb with the ancient practices of the Aztecs, indicating little has changed about the human capacity for violence.