Shared characteristics and concurrent occurrence of rheumatoid arthritis (RA) and spondyloarthropathy in contemporary populations have compromised development of clear diagnostic criteria for distinguishing them. Although modern populations contain individuals with both RA and spondyloarthropathy, ancient populations often manifest only one. The presence of spondyloarthropathy as the sole erosive disease in selected ancient populations allows further clarification of its nature. The tendency towards pauciarticular, asymmetrical involvement, axial involvement and peripheral joint fusion in these populations clarifies diagnosis and distinguishes this phenomenon from RA. The significance of peripheral joint fusion appears to be unequivocally established on the basis of these findings.