SLEIDANUS, JOHANN. – He was the most celebrated annalist of the German Reformation, born probably in 1506 at Schleiden in the Eifel, into the Philippi family. He received his education at Liège; he seems to have studied at Cologne. The first certain document concerning him is a letter from the summer of 1530, in which he reveals himself as an Erasmian humanist, with a warm admiration for Melantone, and perceives in the German religious revolution a firm opposition to imperial policy.
From 1533 he remained for many years in France: he was in Paris with Giovanni Sturm (1534); in November 1538 he enrolled at Orléans for a degree in law, and remained with Cardinal Giovanni du Bellay and his brother Francesco until the death of Francesco I. He was at Hagenau on a secret mission to Filippo, Landgrave of Hesse, and there met with the leaders of the Lutheran movement. In 1544 he was to accompany Cardinal du Bellay to the Diet of Speyer, but they reached only Nancy; S. remained in Strasbourg and translated Butzer’s Short Catechism into Latin. This marked him out to the Landgrave as a possible historian, all the more so because he had collected material on the Schmalkaldic League. He was ambassador in England, where he was able to form friendships and gather information. He was at Trent from the spring of 1551 until April 1552 as an envoy; in 1554 he was with Vergerio. In 1554–55 his major work, De statu religionis et reipublicae Carolo V Caesare commentariorum libri XXVI, was printed at Strasbourg. It was dedicated to Augustus, Elector of Saxony, and was soon prohibited by the Emperor and attacked by Protestants and Catholics alike because, according to Melantone, it recounted much that would have been better left unspoken for ever. S. died on 31 October 1556; in June he had published De quattuor summis imperiis libri III. His minor writings were collected in Opuscula, Hannover 1608.