Complex sentence: Caravaneers paid the taxes in a building called the "Tariff Court", where the Palmyrene tax law dated to 137 was discovered, and it regulated the different tariffs that the merchants had to pay in regard to articles meant for the internal market.
Split into simpler sentences: Caravaneers paid the taxes in a building named the Tariff Court, where the Palmyrene tax law dated to 137 was discovered. The law regulated the different tariffs that the merchants had to pay in regard to the articles meant for the internal market.