Overexploitation leads to the ecological extinction of many oceanic species. The depletion of historical abundances of large animals, such as whales and sea turtles, is well known. However, the magnitude of the historical overfishing of exploited invertebrates is unclear. The lack of rigorous baseline data limits the implementation of efficient management and conservation plans in the marine realm. The precious Mediterranean red coral Corallium rubrum has been intensively exploited since antiquity for its use in jewellery. It shows dramatic signs of overexploitation, with no untouched populations known in shallow waters. Here, we report the discovery of an exceptional red coral population from a previously unexplored shallow underwater cave in Corsica (France) harbouring the largest biomass (by more than 100-fold) reported to date in the Mediterranean. Our findings challenge current assumptions on the pristine state of this emblematic species. Our results suggest that, before intense exploitation, red coral lived in relatively high-density populations with a large proportion of centuries-old colonies, even at very shallow depths. We call for the re-evaluation of the baseline for red coral and question the sustainability of the exploitation of a species that is still common but ecologically (functionally) extinct and in a trajectory of further decline. Overexploitation in the marine realm has been a major driver of the ecological extinction of many species. This loss dramatically altered the functioning and provisioning of services by marine ecosystems 1–3. Large marine animals suffered a dramatic decline relative to their abundance in historical records 3,4. This is the case for many species of whales, fishes and sea turtles 4,5. Marine invertebrates have also been the target of fisheries. Some invertebrate species such as abalone, lobsters and sea-urchins have been exploited during centuries even millennia while for others the fisheries just started to expand recently 6–8. However, for most species, the magnitude of the historical overfishing is unclear. Acquiring precise information of detailed historical baselines is key for setting quantitative targets for guiding conservation goals and management plans. The Mediterranean red coral Corallium rubrum (Linnaeus, 1758) is considered an engineer species (sensu Jones et al. 9) in coralligenous outcrops, which are among the richest but also the most threatened Mediterranean habitats 10. Red coral have been exploited during millennia. Fisheries peaked during the 1800′ when sail and rowing boats were used to drag a heavy wooden cross with attached nets (St. Andrews Cross) over the bottom to entangle coral colonies. During the last century, the use of motorized vessels allowed a replacement of wooden cross for heavy metal bars (up to 1 tm) (ingegno). The use of this gear caused catastrophic impacts in corallige-nous banks 8,11 and its use was banned Mediterranean wide in 1994 12. Since 1950 s' scuba diving allowed to exploit colonies dwelling in areas inaccessible by the dredges such as crevices and caves. At present, scuba diving is the only legal way to harvest red coral. This method still threatens the conservation of this species up to deep habitats