Complex sentence: Later, Treviño discovered news that the Amerindians were again building kivas, their age ‑ old ceremonial houses, and he promoted an investigation by the Franciscan missionaries.
Split into simpler sentences: Later, Treviño discovered news that the Amerindians were again building kivas, their age ‑ old ceremonial houses. Therefore, he promoted an investigation that would be played by the Franciscan missionaries.