Complex sentence: The castle's name comes from a legend about the Roman poet "Virgil", who had a reputation in medieval times as a great sorcerer, that he put a magical egg into the foundations to support the fortifications.
Split into simpler sentences: The castle's name comes from a legend about the Roman poet "Virgil", who had a reputation in medieval times as a great sorcerer. In the legend, Virgil put a magical egg into the foundations to support the fortifications.