A new study finds that the heart of King Richard I was preserved with mercury, mint, frankincense and other plants.

The study is the first biochemical examination into the heart of the king, also known as Richard the Lionheart for his bravery during the Third Crusade. It was led by Philippe Charlier of University Hospital R. Poincaré.

Richard the Lionheart died on April 6, 1199 and was interred in three separate locations. His entrails were buried in the French town of Chalus, his body at Fontevraud Abbey and his heart at the Cathedral of Rouen. At that time it was quite common for hearts to be preserved separately from the body. In the cathedral his heart rested for many years until its discovery in 1838, by which point the heart had turned into a brownish-white dust.

After examining what was left of the heart, researchers were able to detect the presence of several plants, including oak, poplar, pine, myrtle, daisy, mint, plantain and bellflower. Some of the plants, like poplar and bellflower, may have lodged in the casket when the heart was interred. But researchers believe that the others were used as part of the preservation process. Traces of frankincense were also discovered. The heart most likely turned to powder because the lead box in which it was enclosed was not hermetically sealed.

Charlier says that the most alarming find in the study was the discovery of incense in the potpourri, given that it had not been found in earlier preservations. Incense was one of the three gifts offered to Jesus at the time of his birth by the three kings. Charlier theorizes that the incense was intended to provide a direct line between the king and God.

While the discovery may not be groundbreaking, it still provides valuable information.

"It's an interesting curiosity all the same..." says British historian Dan Jones, "to see exactly what ingredients were used."

Bodily preservation during King Richard I's era "is a field of much speculation and, thus, such a study provides some decent evidence," says University of Zurich's Center for Evolutionary Medicine professor Frank Ruhli.

Results of the study were published in Scientific Reports. The heart's remains are being held inside a glass box at Rouen's Departmental Museum of Antiquities. The museum's curator Caroline Dorion-Peyronnet states that it will not be visible to the public.

"Visually, it is not something very pretty to present," she says. "It's dust, it looks like nothing."