Complex sentence: Constructed as a castle in 13th century or earlier, in a gothic style, it was rebuilt in renaissance style in 17th century, in baroque in 18th century and classicist in 19th century; the classicist modernization transformed the castle into what is usually described a palace.
Split into simpler sentences: Constructed as a castle in 13th century or earlier, in a gothic style, it was rebuilt in a renaissance style in the 17th century. The classicist modernization transformed the castle into what is usually described a palace.