The Primarchs have been abducted from the Emperors laboratory when they were still being created. The Chaos Gods then distributed them on different planets. After being reunited with his legions, the planets they landed on became the homeworlds and main recruiting planet of their legions.

If the Primarchs hadn't been transported to these planets, what was the Emperors plan for the Space Marines. I assume, although Terra had quite some humans, they hadn't enough to support 20 legions with such large numbers of high quality humans. Has this ever been discussed / described?

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    By the time the Emperor found the primarchs, their legions were already at reasonable strength
    – Yasskier
    Oct 8, 2019 at 9:45

2 Answers 2


The Emperor did indeed create the initial Legions from Humans largely from terra, when he struck out of the Solar System to seek his lost sons the 20 Legions had been formed.

In fact throughout the Heresy Books one of the recurring points of conflict withint Legions is the Earth Born Legionaires vs those born in the various home systems.

Potentially the Emperor intended for his primarchs to gain legionaries as they expanded, forming recruitment centers throughout the Galaxy as they captured new systems, alternatively maybe he wanted control of the whole process so, as he did with his Thunder Warriors, he could "End the programme" once it had reached its conclusion. But it is not defined anywhere what the plan was.


I can only find low quality information Reddit about where the Legions membership were drawn from before the Primarchs were found, but it is worth thinking again about the scale of the Imperium in the 40K universe.

Terra itself is home to billions.

Terra is perhaps the most massive Hive World within the Imperium, with an uncounted population that numbers several hundred billion human beings. The bulk of Terra's massive population is divided between the upper class that includes the Imperial nobility and Adepts of the Adeptus Terra and the masses of the lower classes who serve as basic labourers.

The elite fighting force of the Space Marines represents a much smaller number of individuals.

The Legions were massive armies, and the size of each could vary tremendously. A precise number was never truly achieved and maintained. Even during the Great Crusade, some Legions were very numerous, while others were not. The numbers would always vary with new recruits and inevitable battle-losses, and also important was the availability of potential recruits and the administrative skills of the Primarch and his officers.

That page gives an estimate of around 2.2million.

It is possible that all space marines were going to be recruited from earth.

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    Nowaday, Terra has Billions over Billions of inhabitants. Back then, it was a war ravaged wasteland and not the centre of an empire. So, they had maybe a billion, 10 billion tops, inhabitants. That plus that only 1 in 10k (max) can become a SM makes, that there could be a max of 1 million astartes. For 20 Legions, so 50k per Legion. But at the height of the crusades, the Legions were around 150k strong.
    – Shade
    Oct 8, 2019 at 10:12
  • @Shade the wiki link above suggests there were 2.2million space marines at the start of the Heresy.
    – Jontia
    Oct 8, 2019 at 10:13
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    The Horus Heresy was 200 years after the Unification. Great Crusade: 798.M30 - 005.M31. When reunited with their Primarchs, some of the figures: Thousand Sons: 1k, Emperors Children: few hundred, Alpha Legion: 1 - 2k. Now, we know that Corax got rid of the Terran SM but had 80k SM when the Dropside Massacre happend. So, 2.2 Million over 20 Legions is around 110 per Legion, if they grew by 80k during the 200 years, they started with 30k.
    – Shade
    Oct 8, 2019 at 11:02
  • @Shade all I've got to go on is the Wiki link as I don't have a lot of primary sources. It specifically puts the number of Thousand Sons at 85k, which I admit is weird, but it has a page reference of pg 154 in Inferno. Ultramarines are 250k and most of the rest 100-150k. Perhaps this is all members of the Legion not just Space Marines? Tech, Remembrancers, Navy?
    – Jontia
    Oct 8, 2019 at 12:27
  • If most were between 100 - 150k and Ultramarines around 250k, that would be fine. Ultramarines are assumed to have absorbed the forgotten Legions. Assuming every Legion started with 50k and were able to add around 80k, then 100 - 150k would be what we get.
    – Shade
    Oct 8, 2019 at 13:13

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