The left bank of the Estuary of Bilbao (Spanish, Margen Izquierda / Basque, Ezkerraldea) is a part of the Greater Bilbao region, its main towns are Barakaldo, Sestao, Santurtzi and Portugalete and besides to the iron mines (Zona Minera or Mehatzaldea), was the heart of the intense industrialisation of Biscay. Thousands of workers from all Spain came to the area during the 20th century to work in the major shipbuilding and steel industries like Altos Hornos de Vizcaya.