No, they're not evidence of some horrible Middle Ages construction-site accident but rather an attempt to keep the dead bodies from turning into vampires.
Bozhidar Dimitrov, head of the National History Museum in the Bulgarian capital, Sofia, said the two skeletons were found last weekend near the Black Sea town of Sozopol.
Dimitrov told the French news agency AFP that the practice was common in some Bulgarian villages up until the first decade of the 20th century.
Dimitrov said superstitious beliefs led to iron rods being hammered through the chest bones and hearts of those who did evil during their lifetimes for fear they would return after death to feast on the blood of the living.
Around 100 similar burials have already been found in Bulgaria.
The pagan rite was also practiced in neighboring Serbia and other Balkan countries.
Vampire legends are widespread across the Balkans. The most famous is that of Romanian count Vlad the Impaler, known as Dracula, who staked his war enemies and drank their blood.
Dimitrov is quoted as saying: "I do not know why an ordinary discovery like that [has] became so popular. Perhaps because of the mysteriousness of the word 'vampire.'"