The '''{{PAGENAME}}''' refers to a series of battles fought in the [[Sol System]] from 010-015.[[M31]] during the closing stages of the [[Horus Heresy]]. The war saw [[Horus]] begin his drive on [[Terra]], capital of the [[Imperium]]. Beginning as infiltration forces  ==Overview=====Imperial Preparations===With the [[Emperor]] preoccupied with the [[War Within the Webway]] and [[Malcador the Sigillite]] waging the [[Shadow Wars]], it was left with [[Imperial Fists]] [[Primarch]] [[Rogal Dorn]] to oversee the defenses of both [[Terra]] and the greater [[Sol System]]. The defenses of the [[Imperial Palace]] were significantly strengthened, and probing raids as much of its aesthetic was destroyed in favor of strategic defensibly.{{Fn|4}} Following the [[Schism of Mars]], [[Kelbor-Hal]]'s [[Dark Mechanicus]] was victorious in claiming the Red Planet, but an Imperial blockade trapped the traitors on their own world.{{Fn|1}} As [[Horus]]' forces inched closer to Terra, Dorn organized the defenses of the Sol System into a series of Spheres. Each consisted of not only Imperial Fists forces on , but also loyalist [[Imperial Army]] and [[Mechanicum]].{{Fn|3}} *The '''First Sphere''' was the outermost defensive zone, commanded by [[Sigismund]].{{Fn|3}}*The '''Second Sphere''' was commanded by [[Halbrecht]].{{Fn|3}}*The '''Third Sphere''' oversaw the blockade of traitor-occupied [[Mars]] . It was commanded by [[Efried]].{{Fn|3}}*The '''Final Sphere''' was [[Terra]] and [[Luna]], overseen by [[Rogal Dorn]] himself. ===The War===For the next several years, the loyalists would counter traitor-instigated uprisings and attempted to break out from their siegebreakouts by the Dark Mechanicus on Mars.{{Fn|1}} The [[Alpha Legion]] announced its entry into the Solar War by exploding the freighter ''Primigenia'' over Terra, killing millions by raining debris. This was accompanied by Alpha Legion organized uprisings at Terra's Damocles Starport and [[Wikipedia: Triton (moon)|Triton]]. All of this culminated in the first major battle of the Solar War, the [[Battle of Pluto]]. The battle saw the [[Alpha Legion]] drive on [[Pluto]], linchpin of the loyalist monitoring of the Sol System. During the battle, a fleet of over 200 Alpha Legion warships assaulted the planet, but after [[Alpharius]] himself was seemingly killed by [[Rogal Dorn]] the conflict traitors retreated.{{Fn|2}}  ===Result===*{{Main|Battle of Terra}}Traitor forces eventually culminated succeeded in driving on humanity's homeworld itself. Thus the stage was set for the legendary climatic [[Siege of Terra]].{{Fn|1}}