In 1443, the Burgundians under Philip the Good conquered Luxembourg. Luxembourg became part of the Burgundian, and later Spanish and Austrian empires (See Spanish Netherlands and Spanish Road) and under those Habsburg administrations Luxembourg Castle was repeatedly strengthened so that by the 16th century, Luxembourg itself was one of the strongest fortifications in Europe. Subsequently, the Burgundians, the Spanish, the French, the Spanish again, the Austrians, the French again, and the Prussians conquered Luxembourg.