Let's do the math.
Option 1: Yeet the corpses off a cliff into a simple pile.
- Average human volume is 0.066m^3. Let's assume they're big people, at 0.1 cubic metres.
- Let's also assume no reduction in volume over time through mummification or decomposition: the pit's frozen, perhaps.
- Bingham mine is a pit about 940m deep and 4km across, and the highest cliff in the world is 1340m high. So we know that a 1km cliff is feasible.
- Assume that the cliff has no karst already at the bottom, and none of it wears down over the millennia. Which is a cheat, but meh.
- To stack up against a cliff, you need a half-cone with whatever angle of repose your material has.
- I'm gonna just go ahead and assume 45 degrees AoR for these frozen bodies. Most stuff is lower, I know nothing that's steeper, and steeper means fewer bodies, so 45 is likely our worst case.
- Volume of a cone is 4 pi r^2 height/3.
- At 45 degrees, height = radius.
- So 4/3 pi cubic km: roughly 4,188,790,200 cubic metres.
- You need 40 billion people to make this pile.
- There are about 7.7 billion people in the world.
- About 110 billion people have ever lived.
Assuming that everyone who ever died was slain by these guards, we would have had to be throwing everyone from the last thousand years at them in order for the pile to have stacked up against the cliff and cause a problem.
So basically, if it's just a few nearby towns, which are having their populations artificially lowered by sending people here to die, then there's no earthly way that they'll ever pile up high enough to be a concern for the guards.
And if you take away the constraints against decomposition and desiccation, the numbers become many times more crazy.
Option 2: the guards can just trample them down as they patrol up and down the path to the gate. This will build up a berm with a walkway on top, and with frozen bodies piled up a little (less than one person-height) either side, of the people who had fallen to the wayside.
Bodies falling in the road would become trampled, raising the roadway with their 0.1m^3 of volume.
The berm would slowly rise from the plain, with sides angled at about 45 degrees, from bodies sliding down from the piles at the roadside. Cross section would be like:
I think the number of bodies needed to build up a section of patrolway would be:
(roadway width + 2 * roadside pile width + height) * height * length * bodiesPerCubicMetre.
So for a 1km long roadway, 10m wide, with 2m piles either side, piled up 100m, that'd be 114M bodies. Not counting the bodies needed for the ramp at beginning and end.
Pile it up to 1km and it's 10Bn, though there'd be definite stability problems before that point, if only because the path width is now greater than the length. Plus, the gate to heaven would probably be buried in bodies by this point.
Option 3: Woodchipper.
So we move it from the frozen tundra to somewhere a little warmer, and make the guards just insanely violent. Or give them access to a wood-chipper, same difference.
There's just not enough of their victims left at the end of the fight to bother with, especially when what's left of them has been marched upon in metal-soled boots a few times.
They are a wet paste which seeps down into the earth, oozes away into the water table, washes away in rain. Yes, eventually all the bonemeal will raise the ground level a little, but not as significantly as the guards' marching wears away the ground, and the angle of repose for rained-on corpse-slime is unlikely to be much more than about a degree, so there won't be a steep hill anywhere.
Crows and rats will likely sup happily on the ooze, but will also shit it out, so won't affect volume much.
Streams might carry some away, but that's just natural erosion and applies to any land over thousands of years.
The bigger problem will be that corpse-ooze will start eventually seeping through the gateway to heaven. If Heaven doesn't want to start stinking on a hot day, there better be a very long stairway to heaven inside the gate.