The Sectai Prosperine are a thrallband of the Thousand Sons Traitor Legion. They were born of individual Thousand Sons sects that banded together in order to reap the benefits of their combined knowledge and power.
The Sectai Prosperine was originally a gathering of minor sects hailing from the fringes of the Thousand Sons hierarchy. In an effort to increase their knowledge and influence alike, the Sorcerers leading these sects banded together as a single organisation, relegating their personal heraldry to symbolic runes and donning the azure, gold and purple of lost Prospero's ruling caste. In combining their efforts, they surpassed all but the greatest of their rivals in terms of power. They now consider themselves the inheritors of Prospero's true legacy, embracing that planet's dark fate instead of running from it as have many of their kin, and believing the destruction of their former homeworld imparted to them knowledge that would otherwise have remained hidden.
The Sectai Prosperine thrallband colours are azure trimmed in gold. The runes upon the tabards of the Sectai Prosperine are laden with meaning, but the colours beneath are often of simpler significance. They hark back to the time when the Sectai was comprised of three autonomous factions -- white for the Learned Mysticae, purple for the Brethren of the Amethyst Sun, and pale green for the Bringers of Spiritual Dawn. The purple colouration common to the Sectai is so widespread it has become part of the macro-cult's identity. Those Chaos Cultists and mutants that serve its Sorcerers will often dye their robes or paint their flesh purple. It has been known for entire thrallbands to change colour at the whim of their Tzeentchian masters.
The Sectai Prosperine thrallband's symbol is a yellow-coloured sigil of the Cult of Knowledge centred upon a field of azure and trimmed in gold.
- Codex Heretic Astartes - Thousand Sons (8th Edition), pg. 23
- War Zone: Fenris - Wrath of Magnus (7th Edition), pp. 126-127