"one shattered gun and one unicorn were left behind"
Sadly the Russians did not have mythical creatures fighting on their side. The unicorns were a kind of gun, a cross between a howitzer and a cannon that could fire cannonballs or shells. They were thus named as the barrel tapered towards the end like a unicorn's horn; until 1805 they had unicorns engraved upon them.
For more on Russian artillery, visit this interesting site.