Complex sentence: In 1234 when the first foreign king, the French Theobald I of Champagne arrived, he did not know Navarrese common law and appointed a commission to write it; that was the first written "fuero".
Split into simpler sentences: In 1234 when the first foreign king, the French Theobald I of Champagne arrived in the area, he did not know Navarrese common law. He appointed a commission to write the laws; this was the first written "fuero".