Mara Yama
The Mara Yama are a nomadic Celestial power treated in The Archimedes Engine less as fully staged characters and more as the external threat that justifies hardline Crown policy — fleet concentrations at Kelowan, annexation talk toward Capo Frois and Uthara, and “dynamic leadership” rhetoric after Thyra’s coup.
Nomads of the citadel
The Mara Yama are terrifying Celestials who live in hidden space citadels rather than ordinary territorial homeworlds. They and the Talloch-Te are nomadic body-plan cousins, and Celestial attitudes place them somewhere between strategic rival and horror story.
Instrument of Crown hardliners
Helena-Thyra cites increasing Mara Yama activity when seizing Wynid. She proposes annexing Capo Frois and the Uthara Dominion (the Mara Yama’s original target before they “stopped” at Hoa Quinzu), false-flag destabilization, and massing all queens’ fleets at Kelowan a decade ahead of a supposed confrontation.
At Hoa Quinzu the Ratarajan warn the Diligent that Mara Yama forces orbit de Verya to refuel — a concrete theatre touch that keeps the threat from being pure propaganda even while Thyra exploits it.
What the novel does not resolve
The book does not deliver a full Mara Yama invasion POV. Their narrative function is pressure: they make hardline expansion and fleet theatre legible, and they keep Capo Frois / Hoa Quinzu on the strategic map when the Diligent flees. How much Mara Yama activity is real, and how much is inflated by Bekket-network politics, is never resolved.