Willis felt his stomach drop as the troop paused at the lip of the canon. The Martians had many flaws but vision wasn’t one of them. The bore of the cannon was wide enough to swallow a motorway and sank so deep into the earth that it’s base was lost in shadows. A small, bright orange elevator cage sat at the edge of the pit, dwarfed by the construction but comfortingly human. 
“Alright, sir?” Sergeant Hobs cut in, clasping a hand on Willis’ shoulder. “Done your sight-seeing?” 
Willis gave a shaky nod. He’d of course seen images of the cannon. There wasn’t a human alive who hadn’t been glued to their TV screens to witness Mankind taking the fight to Mars. Still, seeing the cannon in person was something else. One had to wonder how humanity had survived the wrath of creatures capable of building on such scale. 
“Yes… yes, I’m alright.” He hurried forwards, almost overbalancing in the low gravity, to catch up with the rest of the team. “It’s just a little overwhelming.” 
“Heh, you should have seen this place when we were first landing! The Martians may be dead but their air-defence worked just fine.”
Willis tried not to think on that too much. The Martians were paranoid buggers, their underground cities were ringed with lethal defences, automated turrets, deadfall traps, half-functional robots and other cruel and inventive traps. The orbital cannon, however, lead right into its heart. Perhaps the Martians had not considered a counterattack when building their super-weapon, perhaps they’d no longer cared. 
Within a few moments the team crowded into the elevator and it began its slow descent.
“Did you see much fighting?” Willis asked, clutching onto the railing as the cage rattled and jolted. 
Hobs let out a bark of laughter. “No, the Navy boys stole all the thunder, bombing the place from orbit. Then again, war is better boring. That’s what my grandfather always used to say. He spent a month being shot at by Martian Tripods rather than fighting the Boers like he’d thought; I guess he’d know.” 
“You’ve seen no action?” Willis asked, surprised. 
“Oh plenty of that. The Squids loved their traps, but there was no army waiting for us.” Hobs shrugged, if he was disappointed to come millions of miles to guard archaeologists then he didn’t show it.
Willis started. “They have traps inside their own city?”
“Yup, crazy bastards.”
“Perhaps.” Willis frowned. “Who can say what their motivation was?” 
They settled into an uneasy silence as the car continued to descend. Before too long, the infinite gloom parted and the elevator came to rest above a pile of rubble. A mesh walkway lead into a huge rent in the barrel of the canon. 
“You blasted your way in?” Willis enquired, as they disembarked. 
“Not us.” Hobs shrugged. “Friend in the Navy said it looked like the cannon burst.” 
The party of scientists and soldiers hurried forwards. For a dozen meters they walked through shattered machinery, propped up by the occasional shiny I-beam. The rent opened into a vast atrium and the party paused. 
“Holy…” Willis murmured, staring wide-eyed. Shattered buildings, broken machines and dead bodies were spread as far as the eye could see. “How?” 
“Ever seen a breach in a spaceship?” Hobs said, softly. “The air pulls everything towards the hole. Imagine that happening to a city.” 
Willis shook his head in disbelief. “They destroyed themselves. They destroyed themselves trying to kill us. Why?” 
Hobs snorted. “Well, answering that’s why you boys are here, isn’t it? It’s going to be an easy answer, I can show you all you need.”
“Show me? How?” Willis exclaimed. 
Hobs just smiled and placed a hand on Willis’ shoulder, spinning him in place. A titanic inscription was carved into the wall. In Willis’ broken understanding of Martian it read ‘Those honed in the dark, devour those that grow soft in the sun.’ 
“Monsters, the lot of them,” Hobs declared. “They killed their planet, they tried to kill ours, and in the process killed themselves. We’re better off without them.” 
Willis frowned. He stepped forward to the edge of the rent, pointing his torch at the wall and brushed aside the dust. More writing appeared. “Those that know nothing but darkness, can only extinguish the light,” he read, voice faltering. 
“And what does that mean?” Hobs demanded.
“I can’t imagine.” Willis craned his neck back to take in both the titanic inscription and the scrawled graffiti. “But it seemed someone disagreed.”