Size of the Pre-Heresy Legions

The approximate sizes of a few of the Legions at the start of the Heresy have been provided as follows:

• Ultramarines - 250,000
• Sons of Horus - Between 130,000 and 170,000
• Iron Warriors - 150,000 to 180,000
• World Eaters - 150,000
• Word Bearers - 100,000 to 150,000
• Blood Angels - 120,000
• Night Lords - 90,000 to 120,000
• Iron Hands - 113,000
• Emperor's Children - 110,000
• Imperial Fists - 100,000
• Death Guard - 95,000
• Alpha Legion - Conflicting accounts ranging from 90,000 to 180,000
• Salamanders - 89,000
• Raven Guard - 80,000
• Thousand Sons - 10,000

Circa year 29,811 a catastrophic disaster reduced the number of Emperor's Children to a scant 200 space marines.  The shipment of the Emperor's Children gene-seed was lost en-route to Luna while a mysterious pathogen obliterated the stock held on Terra.

Fortunately, once Fulgrim was located on Chemos in circa year 29,811 the Emperor's Children were finally able to replenish their gene stock.  During years 29,811 to 29,900 the legion began to rebuild their strength with recruits from Terra and Chemos, eventually reaching approximately 110,000 strong. 

Nevertheless, the gene seed catastrophe would have far reaching consequences as it imprinted upon the III Legion an indelible obsession with perfection and improvement.