The Germans are marked by great regional diversity, which makes identifying a single German culture quite difficult. The arts and sciences have for centuries been an important part of German identity. The Age of Enlightenment and the Romantic era saw a notable flourishing of German culture. Germans of this period who contributed significantly to the arts and sciences include the writers Johann Wolfgang von Goethe, Friedrich Schiller, Johann Gottfried Herder, Friedrich Hölderlin, E. T. A. Hoffmann, Heinrich Heine, Novalis and the Brothers Grimm, the philosopher Immanuel Kant, the architect Karl Friedrich Schinkel, the painter Caspar David Friedrich, and the composers Johann Sebastian Bach, Ludwig van Beethoven, Wolfgang Amadeus Mozart, Joseph Haydn, Johannes Brahms, Franz Schubert, Richard Strauss and Richard Wagner.