Calth - History: Calth was originally a verdant Agri-World whose manufacturing output at the time of the Great Crusade would have rivalled that of Macragge in only two to three more solar decades if the Horus Heresy had not intervened to push the planet down a radically different developmental path. There was even talk of constructing a superorbital ring like that which encircled Terra and was intended to get cargo to and from orbit as quickly and inexpensively as possible. The most important and heavily populated worlds of the Imperium had all constructed similar rings at the time, which were marvels of human technology and engineering and symbols of the new Golden Age that the Emperor intended to create for Mankind.On the eve of the Calth Conjunction before the start of the Battle of Calth, Calth was held by many as an as-yet uncut jewel in the crown of Ultramar, a glittering example of the future. It was long planned that Calth would take its place amongst the greatest of the Five Hundred Worlds and that its name would be known not just within Ultramar, but across the entire Imperium of Mankind.To that end, since its settlement just a few short generations before the outbreak of the galactic civil war, Calth's infrastructure was rapidly expanded in expectation of future growth. Many of its cities were built as mighty arcologies -- self-sustained centres of habitation and production. Many of these arcologies were built within the extensive network of subterranean chambers and tunnels for which the world had become renowned and many housed millions of workers. These centres of population were naturally protected from the extra-seasonal solar storms which assailed the world approximately every fifteen years, and hosted additional shelters to accommodate surface dwellers forced below during especially heavy periods of coronal massed ejection.In orbit above Calth was one of the most extensive orbital docking, repair and resupply facilities in the entire Five Hundred Worlds and beyond. This facility was built in expectation of future expansion far beyond the extent of Ultramar, and was due to see its most auspicious use to date with the Calth Conjunction -- the mustering of the combine fleets of the Legiones Astartes Word Bearers and Ultramarines in preparation for a joint attack against the Orks of Ghaslaskh xeno-hold. Being a strategically vital node in the infrastructure of the Five Hundred Worlds, Calth was heavily protected by a planetary defence network far in excess of most Imperial planets. This grid integrated over nine hundred orbital defence platforms and thousands of ground cities, from defence laser silos to interceptor launch pads, into one of the most potent defensive networks in the entire Segmentum.The true value of Calth to the Five Hundred Worlds, and the reason for the massive investment in resources committed to it; was as a potent symbol of Mankind's future. As the Great Crusade drew to a close, the Primarch Horus taking the mantle of Warmaster while the Emperor of Mankind returned to Terra to oversee the next stage in the expansion of the Imperium, great leaders such as Lord Guilliman looked to their own role in that future. The people of Ultramar were immeasurably proud of the realm they had built and looked to a bright future in which Ultramar and the greater Imperium watched benevolently over a galaxy re-shaped by the sacrifice and toil of two centuries of conquest. Calth intended to join Macragge, Saramanth, Konor, Occluda and Iax as the most important worlds of the Ultramar Sector, whose influence already extended across a vast swathe of the Imperium's Segmentum Ultima. It stands as one tragedy among countless others that this future would never be realised, due to the perfidy of Warmaster Horus and the Traitor Legiones Astartes.