Trás-os-Montes was one of the 13 regions of continental Portugal identified by geographer Amorim Girão, in a study published between 1927 and 1930.
Together with Alto Douro it formed Trás-os-Montes e Alto Douro Province.
Geomorphologically the mountainous Trás-os-Montes region forms a continuum with the Galician Massif, so that it is considered as a whole under the name 'Galicia-Trás-os-Montes Zone'.
References
Trás-os-Montes (region) Wikipedia(Text) CC BY-SA