If an Imperial Starship did a threesome with an Imperial Fortress and a Baneblade, then their baby would be the Capitol Imperialis. Or in simpler terms, think of a landship that could run over a Warlord Titan. This vehicle is by far one of the largest mobile land weapons platform in the Imperium's history, dwarfing almost anything short of the largest Titan. Although due to its size and apparent snail-paced speed, this massive hunk of Imperium "FUCK YOU!" is only used as a mobile HQ and base of operations. However, due to these implications, they are notoriously expensive in both resources and technology and are thus rarely ever used in actual engagement.
Not to be confused with the Leviathan which is another oversized Imperial tin-can and the Cyclops and Colossus which are the Squats own indigenous landships in which the Imperium shamelessly ripped-off in design.
As mentioned before, standing at 50 meters tall and 100 meters long, this behemoth of a landship is one of the largest land combat vehicles in the IoM, it is so large that two entire companies of Imperium Red Shirts could fit snuggly inside. Due to its nature as a mobile command base, the Capitol Imperialis is only used in a defensive manner being rarely seen in actual combat, in order to protect it from outside assault, the Capitol Imperialis is equipped with one of the most ridiculous defenses the Imperium can muster. Examples include having its outer hull plated in pure solid Adamantium as well as six fucking void shield generators for extra protection! Because quite frankly having just one Void Shield just isn't enough to make this oversized tin-can more secure enough.
Just like most oversized vehicles in the Imperium the Capitol Imperialis has a command bridge. This command bridge is situated deep within the belly of the beast and gives the regiment's commander the tools needed to command his troops effectively without really needing to actually go out in the middle of the battlefield with a chance of having his head blown off. The bridge also features all your usual equipment such as vox-gears, pict-casters, logic-engines, and a holo-map which in turn is constantly inspected by its crew of Servitors that gather, analyze, and display information to allow the Imperial commanders to carry out their massive dick-waving contest.
Of course to give you a sense of scale on how large space battles are compared to land battles in WH40K. As big as the Capitol Imperialis is, it is only roughly the size of one Fleet base Macrocannon. Yeah....only the Land Ships of Zayth and the maximum estimated size of the Ordinatus Armageddon can compete in the weight department. Of course there are other land vehicles in the Imperium that can rival the ships in the Imperial Navy, they just haven't got enough screentime yet since their all classified as civilian transports and thus, not Grimderp enough.
Of course being such an important asset in the Imperium's arsenal, the Capitol Imperialis requires plenty of Dakka in order to make the enemies of the IoM to justifiably shit themselves in fear. Armed with a massive Macrocannon called the Behemoth Cannon, this cannon is so large that four entire Leman Russ Battle Tanks could fit inside the barrel with room to spare, seriously we aren't joking that this thing has enough Dakka to cause fucking avalanches and propel enemy vehicles hundreds of meters into the air like some kind of deranged demon baby.
Other side weapons include an assorted amount of hull-mounted twin-linked Heavy Bolters for close defense and an electrically charged outer hull for those critters that like to get close and personal.