Complex sentence: The building of the great public bridges was a continuous topic of political controversy in the city, and the discussion about construction materials--stone or iron--was a reflection of the dispute between Berne's conservative and liberal factions.
Split into simpler sentences: The building of the great public bridges was a continuous topic of political controversy in the city. The disputes about their location and even their construction materials--stone or iron--were a reflection of the clash between Berne's conservative and liberal factions.