The history of the territory of the Union is inextricably linked to the history of mining development of the coastal range of Cartagena-La Union.

Mining tools from Roman times. Archaeological Museum of La Union, in Portman.

The oldest settlement in the municipality is located in the hamlet of Portman, a name whose origin is not a course or Catalanised Port Catalan Many, but in a romance or Port Man Port Magn prior to the Catalan presence and stagnant in their development phonetics for being transmitted by the Arabs during the Muslim occupation (as is attested Burtuman al-Kabir, 'Burtumán the Great'), with the Latin etymon remote Magnu Portuguese dialect and this in turn classical grammar as Portus Magnus, result which eventually influenced the local dialect phonetic Murcia voice pronounces the Pormán or Polman.

Across the mountain mining archaeological sites abound that attest to the exploitation of mines since time immemorial. For the port of Portman, mines Carthago Nova Roman ingots were exported silver, lead, iron, zinc and other minerals throughout the Empire.

Due to rapid fat and mineral development in the nineteenth century, corporations pedáneas of Garbanzal, Blacksmith and Portman decided to secede from Cartagena to merge in own municipality and City Council with the name of Villa El Garbanzal (January 1, 1860 .)

Old public market. Eclectic-modern architecture of Victor Beltrí.

Portman then continue to serve as a mining port.

Soon, however, disputes between the inhabitants of the main settlements (Garbanzal and Blacksmith) led to the renaming of the young municipality, which would be called "The Union" from 1868. In 1894, the town would receive the title of city. A considerable immigration of Andalusians Almeria, Jaen and Granada, who came to work in the mines of the town, contributed to the ethno-cultural special character of the city, certainly akin to that of eastern Andalusia (especially regarding the singing of the mines - cante jondo).