Evidence of horse riding in domestic horses during the Bronze Age in Iberia

The adoption of horse for transport purposes profoundly reshaped mobility, exchange, and socio-economic organization, yet identifying early ridden and/or transport horses in Iberian archaeological contexts remains challenging due to the poor preservation of tack and other perishable equipment. Here we present an exceptional equine cranial specimen of 17 to 20 years of age at death from the Late Bronze Age site of Castillo Reyes (Pinto, Madrid, central Iberia), assigned to the Cogotas I horizon and directly dated by radiocarbon. The rostral skull fragment displays a well-developed groove on the dorsal margin and medial surface and two additional shallow and more rostral grooves on the lateral side of the nasal process of the incisive bone. This feature is consistent with mechanically induced bone remodelling linked to prolonged pressure and friction in the nasal region, as documented in modern ridden horses and interpreted as a marker associated with early bridle/noseband control. The specimen was analysed using radiography, multidetector computed tomography, and 3D volume rendering to quantify position (relative to the nasoincisive notch) and incisival length and maximum depth of the caudal groove. In addition, sequential stable isotope analyses of adult horse tooth enamel were conducted at millimetre-scale resolution, yielding 179 paired measurements of enamel carbonate δ 13 C and δ 18 O. Enamel δ 13 C values indicate a diet dominated by C 3 plant resources, whereas enamel δ 18 O exhibits wide intra- and inter-individual variability. Several horses show isotopically homogeneous profiles consistent with local residency, while others present structured intradental shifts incompatible with sustained formation under a single local water signature, supporting individual mobility across climatically distinct regions. Taken together, osteological and isotopic evidence indicates the presence of domesticated, ridden and/or transport horses and mixed local/non-local individuals at Castillo Reyes during the Late Bronze Age, highlighting the value of integrating cranial activity markers and sequential enamel isotopes to reconstruct early horse management, movement, and exchange in Iberia.