Rumble.
A rumble could be heard in the distance. A sound like thunder. High up, the sun's rays were slowly but surely blocked by dark, ominous clouds. As that happened, a shadow fell over the land, a dark sign of what was about to happen. The troops waited, having been posted to block the road from a possible attack.
Rumble.
A cloud of dust could be seen on the horizon, hard to make out in the dim light. The soldiers stiffened, sensing a possible threat. It started drizzling, then quickly escalated into a heavy downpour. Lightning flashed, a jagged line splitting the sky into two dark halves.
Rumble.
The dust cloud hid the things that were causing it. Ten thousand hoofs charged across the earth, making a terrifying sound that sounded like thunder, but was a lot more potent. The horsemen approached the army, starting their charge at one kilometer from the soldiers sent to block the path.
Sensing that an attack was imminent, the commander of the defending soldiers ordered his soldiers to form up in a solid line. They did so in a formation that featured overlapping shields, and spears bristling from everywhere. A calvary charge would break into pieces upon it.
Six hundred metres from the shield wall, the horsemen reached their full speed.
The soldiers confidently waited.
Five hundred metres away, they unslung bows from saddle hooks.
The soldiers confidently waited.
Four hundred metres away, they notched arrows and bent their bows.
The soldiers confidently waited.
Three hundred metres away, and a black wave of arrows soared through the air, thudding into shields and even penetrating some, but dealing minimal damage only.
The soldiers were not so confident now, and waited impatiently for the enemy to appear. Had archers fired upon them? Or did the horsemen dismount to use the bow?
Every six seconds, a volley of black shafts would smash into the lines of the defenders, with more and more devastating results. At first, only the shields were penetrated, and few fell to the intense storm of arrows thanks to their armour. A couple of volleys later, the arrows punched through armour and shield with ease, shredding the armour of the defenders and sending them into disarray. Then, as the demoralised defenders tried to protect themselves, the attackers stopped fifty metres away from the defenders and rained arrows upon them, a rain that was more destructive than the natural one falling.
The desperate survivors, decimated by arrows that seemingly originated from nowhere and blinded by rain, tried to retreat, but the horsemen discarded their bows, and drew swords as one. They rode down the survivors and methodically hacked every last one into pieces. The road was now clear, but there were bodies ripe for looting before they moved on.
The commander of the horsemen looked proudly at his force. With it, he would conquer the world.