In 1811 he married Brentano's sister, the famous Bettina, and thenceforward lived partly in Berlin and partly on his estate of Wiepersdorf in Brandenburg. He kept his Romanticism out of his private life; he was a sane, healthy human being, a clever farmer, a sober Protestant and Prussian. Eichendorff describes him as follows: "Handsome and distinguished looking, frank, ardent, and yet gentle, honourable and reliable in all things, faithful to his friends even when every one else deserted them, Arnim was in reality what others, by dint of a sort of mediæval polish, strove to appear--a knightly figure in the best sense of the word; but for this very reason it always seemed to his contemporaries that there was something strange and out of place about him." Something strange there must certainly have been in his nature, for, staid and sober, calm and harmonious as was his life, his writings give us the impression of restlessness and complexity. He himself was cast in one piece, his works never are. Besides plays, now unreadable, he wrote two long novels and a number of short tales, which all bear witness to the fantast in him. The epithet "fantast" may be equally suitably applied to Brentano. The first conspicuous difference between the two is, that, whereas Brentano's strength lies in his naïveté and his childlike fancies, Arnim is profoundly serious even in his wildest flights. With all his love for the popular, with all his eagerness to open the eyes of the cultured to the beauty of the simple and childlike, he remained the dignified aristocrat in his own writings; he never let himself go as Brentano did. When his muse has a paroxysm of madness, it is cold, almost severe insanity, not a fiery, merry frenzy, like that to which Brentano's muse is subject.