http://archaeologyinbulgaria.com/2016/11/24/archaeologists-discover-unknown-fortress-walls-byzantine-gold-coin-in-rusocastro-fortress-near-bulgarias-kameno/
Best known for the AD 1332 Battle of Rusocastro, in which perhaps 14,000 Bulgars crushed 3,000 Byzantines. Wikipedia article (with slightly confused numbers) here (https://en.wikipedia.org/wiki/Battle_of_Rusokastro).