Late Roman times imprinted with instability, and a consequent decline in large urban centres. In contrast, urbanization seems to have increased in Augusta Emerita (today Mérida), capital of Lusitania, because of the attractive commercial position of this powerful Christian centre. A mixed of beliefs, cultural and social backgrounds was coexisting at the core. These facts could have conditioned diet, perhaps becoming different from the surrounding rural areas, or increasing heterogeneity inside the capital. We reconstructed the diet of the largest Late Roman necropolis of Mérida, the Ampliación del MNAR (3rd -5th centuries AD), whose burial rites have been classified as no-Christian. A total of 70 humans (29 males, 14 females, 23 non-adults) were analysed for δ13Ccol and δ15Ncol to compare their isotopic values in bone with those of 14 animals: 6 sheep/goat, 5 cattle, 2 pigs and 1 horse. Faunal and human isotopic results indicate a trophic chain based on C3 plants. Humans over 12 years old (δ13C=19.2 ± 0.8‰, δ15N = 10.2 ± 1.3‰) seem to have had lower consumption of animal protein and C4 plants than other populations from rural sites, although general diet was rather homogeneous in Hispania. Three outliers, one with important intake of C4 plants, have been identified. Medium animal protein diet reconstructed by stable isotopes and relatively low presence of pathological markers, contrast with high infant mortality, suggesting minor stress in early life. If confirmed, limited diet might be linked to the marginal situation of pagan people in a well christianised Augusta Emerita, but much likely being a consequence of the decline of urban centres during Late Roman times.