Complex sentence: The museum was a result of the work carried out by the Comisión Pro-Museo Histórico-Arqueológico (Commission for the Historical and Archaeological Museum) which had gathered items found on construction sites around the city and provided a basis for promoting cultural heritage.
Split into simpler sentences: The museum was a result of the work carried out by the Comisión Pro-Museo Histórico-Arqueológico (Commission for the Historical and Archaeological Museum). It had gathered items found at construction sites around the city, which provided a basis for promoting cultural heritage.