Meridian is an Imperial Hive World and the capital world of the Sub-sector Aurelia of the Korianis Sector in the Ultima Segmentum. It features huge city-spires rising from urban landscapes the size of continents. Meridian's ancient manufactorum hive city, Angel Forge, produces everything from household goods to Lasguns and Imperial aircraft and is the most important manufacturing facility in its sector. As a major industrial power, Meridian plays a vital role in the Aurelian Sub-sector, accounting for over 90% of the total population and economic output of the entire sub-sector. It is for this reason alone that the Imperial Governor of the Aurelia Sub-sector treats the other planets under his rule as nothing more than a source of unending resources for Meridian's industrial complex. This ensures that Meridian maintains links with the Imperium at large.
Sergeant Thaddeus of the Blood Ravens Chapter was originally the leader of an underhive gang on Meridian. Before him, no native of Meridian had been recruited by the Blood Ravens for 700 standard years, because its people were regarded as physically weak and morally decadent by the rest of the sub-sector. Thaddeus' recruitment to the Blood Ravens, on the recommendation of Captain Davian Thule, was regarded with skepticism by the rest of the Chapter, but his hive-ganger instincts proved to serve him well once he became the leader of an Assault Squad.
The constant battles of the last standard decade and the Three Aurelian Crusades have taken their toll on this beleaguered Hive World and placed it in constant turmoil. Riots for basic supplies in the lower-spires are constant and widespread, and the planet's Planetary Defence Forces are stretched too thin with threats both at home and throughout the sub-sector. The inevitable low morale and exhaustion of the PDF has led to rampant mutiny, desertion, and far worse, heresy. The intervention of outside Imperial forces proved necessary, and regiments of Cadian Shock Troops have been brought in to maintain control and discipline. Despite this, the machinations of Chaos continue to inspire corruption and heresy, picking away at Meridian's resolve.
Sometime during the late 41st Millennium, in what became known as the First Aurelian Crusade, a splinter fleet of Hive Fleet Leviathan entered Sub-sector Aurelia intent on devouring all of its worlds. A Blood Ravens Chapter task force was sent to defend the vital star system from the encroachment of the Tyranid menace. Meridian was the target of constant Eldar attacks and it was ultimately revealed that the Farseer Idranel of Craftworld Ulthwé had been planning to lure the entire splinter Hive Fleet to Meridian using the world's human population as bait. Then the Farseer planned to destroy it to eliminate the Tyranid threat to her own Craftworld but at the expense of destroying a vital source of manufacturing for the Blood Ravens and billions of human lives. Gregor Vandis, Meridian's Planetary Governor, largely ignored the Ork and Eldar activity amongst his people, until the Eldar raided a warehouse belonging to House Vandis, which contained pilfered Blood Ravens Chapter relics recovered from Typhon Primaris. With the dire threat of the Tyranids revealed, the Governor abandoned the planet and fled, leaving his subordinate adjutant, Administrator Elena Derosa, in charge.
Though she lacked vital intelligence, Acting Planetary Governor Derosa attempted to coordinate with the Blood Ravens task force in order to combat the xenos threat. When the Tyranid threat was fully revealed, she assumed the full Governorship of Meridian and allowed full access to Angel Forge to the Blood Ravens. The Space Marines were able to manufacture the necessary armaments and weapons needed to combat the Tyranids. Captain Gabriel Angelos and an entire company of Blood Ravens landed on the battlefield from the recently arrived Strike Cruiser Litany of Fury and defended the beleaguered Aurelian Blood Ravens strike force from the oncoming swarms of Tyranids. Angelos himself joined the Aurelian Force Commander Aramas' strike force and his aid proved decisive in killing the Hive Tyrant Alpha who was controlling the swarm. With the Hive Tyrant Alpha dead, the Tyranid swarms became uncontrolled by the Hive Mind and turned on each other even as the Bio-Ships in orbit fell ill and died. The Blood Ravens had won the day and the Sub-sector Aurelia and its billions of people had been saved from complete annihilation by the Great Devourer.
Following the Tyranid invasion of what became known as the First Aurelian Crusade, Governor Derosa continued to serve in her new post, though she was barely trusted by the planet's ruling aristocracy. Several of these noble houses would later be recruited by the Black Legion during the Second Aurelian Crusade, turning their private house armies to the service of the Ruinous Powers. Led by the traitorous personal militias of House Vandis, these forces took control of Meridian by overrunning the Capital Spire. Governor Derosa's 85th Vendoland Regiment managed to combat the Traitors during multiple battles across the planet but sustained heavy casualties at each one, culminating the Loyalists' last stand at the Meridian Imperial Palace. Derosa called the Blood Ravens for aid when it became apparent that she and her forces would not be able to triumph without aid. Even though Blood Ravens Captains Gabriel Angelos and Apollo Diomedes did not answer her call personally, they despatched a force of their fellow Astartes to Meridian and with their assistance Governor Derosa's forces managed to defend the palace and emerge victorious, though the world remained a seething pit of rebellion until after the end of the Third Aurelian Crusade.
As a typical Imperial Hive World, Meridian is ruled by a wealthy feudal aristocracy that dominates the upper levels of its hive cities and are the owners of the enterprises that comprise the planetary economy. The use of the Angel Forge facility is highly bureaucratic and follows a strict schedule of use set by the planet's governor and their Privy Council years in advance. The Meridian elite of these upper hive spires remains largely indifferent, or ignorant, of the billions of middle and working-class citizens who inhabit the lower levels of all the other hive cities on the planet. Among these lower levels, competition for scarce food, clean water and the other necessities and luxuries of Imperial life can be brutal. Food riots and savage gang warfare are particularly frequent in the lowest regions of these cities, known as the underhive.
In the novel Dawn of War II by Chris Roberson, Planetary Governor Gregor Vandis is caught by Sergeant Aramus (who served as the PC game's Force Commander character in the novels) with a large collection of alien and Chaos artefacts, as well as a cache of Blood Ravens Chapter relics. Among these relics was the Power Sword once wielded by Captain Davian Thule. Instead of fleeing the planet as he did in the events of the PC game, Vandis was executed on the spot by Aramus for his heresy and grave affront to the honour of the Blood Ravens.