It took until book 6 to finally read Chris’ part of the siege. Finally, since 91, I got my answer as to why the great khan didn’t partake on the assault, with the Emperor, against Horus. A noble, valiant defiant stand in the face of annihilation, the White Scars prove that they are their own legion, standing apart from all others, in a way that makes sense. The canon was in good hands with this book. Plus- Sigismund! He has redeemed himself from prior shortcomings during the siege- my man!