The elemental analyses of the white powder found a huge quantity of lead, obviously originating from the reliquary, explaining also the presence of tin, antimony and bismuth, classically found in poorly purified lead15 from the Middle Ages16. Iron may also be attributed to iron hardware of the reliquary. On the contrary, mercury is attested in embalming both in literature and in Medieval and Renaissance mummification practices; for example, Guglielmo of Saliceto in his Chirurgia (1275 ca) and the French surgeons Henri de Mondeville (La chirurgie, 1306–1320) and Guy de Chauliac (La grande chirurgie, 1363) refer to the use of “quicksilver” in the post-mortem treatment of bodies; more, mercury was found in the burial of Jean de Lancastre, duke of Bedford (died 1435) in the Rouen cathedral17 and in the burials of the French Queen Anne de Bretagne (died 1514) and the French King Charles VII (died 1461) in the St Denis basilica18. In 1866, at the first opening of the grave of the Duke of Bedford, metallic mercury was found in great quantity (11.25% of the mass, i.e. 112,500 μg/g). Non-metallic mercury was not determined. Fifty-two years later, a new and more complete analysis performed by Le Roy showed that total mercury represented 8.03% (80,300 μg/g) of the solid mass and metallic mercury only 4.08% (40,800 μg/g), the rest (3.85% or 38,500 μg/g) being in a combined form17. Then, more than fifty years after, 36% of the metallic mercury had disappeared. After several experiments, Le Roy concluded that mercury must have been employed as an emulsion of metallic mercury in a balsamic-like substance17. The amount of mercury found in Richard's heart (150 μg/g), even if considerably less than the levels observed in the rest of the Duke of Bedford, may indicate the use of another mercury compound such as mercury chloride (calomel); it cannot be considered in any case as originating from lead impurities, as it is never retrieved in ancient lead15.

Pollen grains recorded in the heart powder may originate from embalming products and/or airborne contamination. The interpretation of such results needs a comparison with Medieval and Renaissance literature about plants and vegetable substances used during the embalming process, but also with the period and localization of the preparation of the cadaver of King Richard I. Some pollen grains must undoubtedly be considered as originating from embalming products (myrtle, daisy, mint), whose pollination occurs long before/after Spring; they also may have been stored before their use during the embalming process (that occurred short after the 6th of April 1199)7,8,9,10. It is noteworthy that their state of preservation is better than the other recorded pollen grains (Table 1): pine, Holm oak, plantain. That may indicate some transport by air and the resulting oxidation. They are hence considered as contaminated external material, excluding their use during the embalming process, as pine resin is also a substance attested in embalming, for example in the treatise La practica in arte chirurgica copiosa by Giovanni da Vigo (1450–1525)19. Two other pollen grains, even if we consider them as external contaminations, are well preserved: poplar (characterised by a fragile pollen) and bellflower. Poplar and bellflower were blooming at the time of the death and embalming of the King. Accordingly, we interpret their presence in a so good preservation state in relation with the short time-interval between their pollination and contamination of the heart contain and probably their nearby distribution (i.e. short transport and weak risk of oxidation).

Molecular analyses showed the presence of frankincense (corresponding to the white matter) and wood tar product, creosote type (corresponding to the dark one)13. Frankincense was a non-negligible part of all embalming process during medieval times14, as this symbolic substance appeared at both extremities of the Christ life: presented by the Biblical Magi at His birth and used during His external embalming after the Passion.

The goal of using such materials was to allow long-term conservation of the tissues and good-smelling close to the one of Christ (comparable to the odour of sanctity)20. Comparable examples from later periods (13th to 19th c.) have been described, particularly in Italy: Cangrande della Scala (1291–1329)21,22, members of the Medici family in Florence23, the Aragonese mummies in San Domenico Maggiore, Naples24,25, the Blessed Christine of Spoleto (1432–1458)26, Salimbene Capacci (1433–1497) and his wife Margherita Sozzini (died in 1511)19, late Medieval and Renaissance Saints27, etc. Comparable substances and plants known as filling materials of these mummies have been described (mint, rose powder, myrtle, etc.), but the case of Richard I may represent the oldest physical example of their use during an embalming process. Daisy and incense (oliban) have not yet been described in other cases of mummified corpse or anatomical fragment.

In addition, it is important to mention that even if the heart was completely pulverized at the time of our examination (and of its discovery in the 19th c.), it does not mean that the embalming was not successful, just that the equilibrium was lost between the mummified organ and its direct environment due to the alteration of the metal box and water infiltrations from the ground.

The use of such conservation products above-mentioned, reveals the influence of cooking and pharmacy for the embalming of viscera and particularly the heart. Indeed, the first embalmers (12th c. AD) were cooks, i.e. those who were used to open the meat and cut the offal, but also had access to herbs, spices and other odoriferous substances28. Then it was the turn of apothecaries and afterwards, chemists29, using plants, sometimes exotic and disinfectant solutions proved to be efficient for the medium and long-term conservation of human cadavers after their opening by surgeons and barbers3.

This embalming process in the case of King Richard was, first of all, necessary for practical reasons: the organs were treated because the King's body had to reach the definitive burial (Rouen) which was far from the death place (Châlus): almost 530 kilometres. Other reasons, political this time, could have motivated this partition of the body, such as the appropriation of a territory using physical parts of the King30,31,32,33. In the case of the controversial life of Richard I, it is equally possible that the post-mortem treatment of the organs (and particularly the heart), inspired by biblical spices, was necessary in order to accelerate his religious apotheosis. Indeed, as stated by a 13th century bishop of Rochester34,35, Richard the Lionheart spent 33 years in Purgatory as expiation for his sins and ascended to Heaven only in March 1232.

With embalming, symbolically, the deceased is identified as the Christ whose body was scented with spices by Joseph of Arimathea before being placed in his tomb. This study conducted on the mummified heart of Richard the Lionheart (died 1199) made it possible to ascertain that the organ has been filled or covered with a mix of vegetal and mineral material. Since the studied organ was entirely turned into powder, we ignore if an opening of the heart occurred prior to any embalming and the exact aspect of the embalming material (liquid and/or salts).

This embalming method is of great importance, as we do not have any procedure or surgical treatise known for this period (end of the 12th c. AD.) describing the methodology and/or composition of the embalming material.