The architecture of the cattle-breeders of Lemnos is an Unknown Architecture that it is usually passed by without being evaluated. The products of this architecture are called mandres (= pens) not only on Lemnos but throughout the Aegean as well. They are made of simple materials, stone, wood and canes and their building technique remains unchanged in the span of 4000 years -from the Prehistoric period until today- as unaltered are the needs these structures serve. Still today on Lemnos hundreds of such buildings welcome and shelter the shepherd and his flock. On the basis of the cattle character of the area -pure or mixed- and the capacity of the flock the mandres are divided in five types: Type A: Original, B: Agricultural, C: Agricultural-Cattle, D: Cattle, E: Family. The thorough analysis of each type offers the possibility not only the building and compositional ability of its creator to be studied but mainly the way of living in past, old times to be known and understood.