The gang of three broke into the museum archives building in Dublin late on Wednesday, tied up a security guard and loaded four rhino heads -- each with two horns --- onto a van, police said.
Thinkstock1 of 10
Thinkstock2 of 10
Thinkstock3 of 10
Thinkstock4 of 10
Thinkstock5 of 10
Thinkstock6 of 10
Thinkstock7 of 10
Thinkstock8 of 10
Thinkstock9 of 10
Thinkstock10 of 10
The guard, who was unhurt, eventually freed himself and raised the alarm, but not before the thieves had made off with their haul.
RELATED: Bomb-Sniffing Dogs Work Tirelessly In Boston
Rhino horns have become increasingly valuable as a component of traditional medicines in Asia, where they are falsely believed to have powerful healing properties.
Poachers feeding the lucrative market have decimated rhino populations across Africa -- in South Africa, more than 200 of the animals have been killed so far this year.
RELATED: 35-Year-Old Goldfish Has Died, Leaving Lifelong Tank Buddy Behind
A spokeswoman for the Irish museum said fears about a possible theft had prompted curators to move the horns from public display last year into storage.
"Their price is based on weight and the total amount stolen could have a street value in the region of 500,000 euros," she said.
RELATED: Cat Survives Getting Accidentally Buried Alive
Police said they had begun an investigation into the theft, adding: "The crime scene is sealed off for forensic technical examination."
Woman Has Incredible Bond With Orphan Rhino: