A Thracian mask helmet dating back to the first century and stolen some 20 years ago, can now be seen once again on display in the Archaeological Museum in Plovdiv. Made of iron and silver the mask belonged to a Thracian nobleman and was discovered during archeological excavations in a burial mound in 1905. There are just three such preserved masks in the world, as the others are in Italy and France. Experts say the price of the mask helmet is between two and three million euros. In 1995, two armed robbers stole the mask without paying any interest to 600 gold coins next to it, so it is assumed that the theft was ordered by a collector. The unique mask was returned to Bulgaria after an operation of the State Agency for National Security aimed at combating trafficking in cultural property.