In 371 AL the outermost Farsight beacon of the Deep Space Explorers stopped transmitting. Then the next one, and the one after that. The line of silence moved inward at a steady, unhurried pace.
The first Harvester swarms reached the Rim mining stations eleven weeks later. They did not negotiate, and they did not take prisoners. They took the stations, the asteroids the stations were mining and, in several cases, the moons those asteroids orbited. The Explorers matched the bio-signatures against the oldest records in their archives, the fragmentary logs of the pathfinder crews from the Long Dark. The match was exact. The Tide had found humanity again.
The Iron Vanguard met it at the Grey Verge, in the battle the Frontier remembers as the Rim Burning. The Vanguard held for nineteen days against a swarm that did not tire, did not retreat and grew back what it lost. On the twentieth day the line broke for the first time in the Vanguard's history. The legions fell back, fighting, to the inner systems. One flag officer brought her entire squadron home: a young commodore named Selene Voss.
Then, as suddenly as it had come, the Tide stopped. It did not retreat. It simply settled into the systems it had taken, grew its hives, and waited. Frontier Command's analysts have argued about why ever since.
“It did not beat us. It did not even try. It just kept coming until there was nothing left to hold the line with.”
— Commodore Selene Voss, after-action report, the Grey Verge