Complex sentence: At that time was the main source of livelihood of the people, and Llerena, gradually is becoming the natural center of the region and its walls housed the most important Masters of the Order of Santiago, who choose it as a temporary residence.
Split into simpler sentences: At that time was the main source of livelihood of the people, and Llerena, gradually is becoming the natural center of the region. Its walls housed the most important Masters of the Order of Santiago, who choose it as a temporary residence.