His next treatise, Liber apologeticus de arbitrii libertate, was written during his stay in Palestine, and in connexion with the controversy which engaged him there.
His Apologeticus, a defence of the papal claims against the Empire, written - as is supposed - in refutation of Piero della Vigna's argument in favour of the independence of the Empire, has been lost.
It is certain that he was settled in Carthage in the second half of 197, the date of his writing his Apologeticus and (shortly afterwards) his two books Ad nationes; we also know that he became a presbyter in Carthage and was married.
- To this class belong the Apologeticus (197) and the two books Ad nationes, De spectaculis, De idololatria, De cultu feminarum Libri II., De testimonio animae (written soon after the Apologeticus), Ad.
The Apologeticus, which in the 3rd century was translated into Greek, is the weightiest work in defence of Christianity of the first two centuries.
Seckendorf's principal works were the following: - Teutscher Farstenstaat (1656 and 1678), a handbook of German public law; Der Christenstaat (1685), partly an apology for Christianity and partly suggestions for the reformation of the church, founded on Pascal's Pensees and embodying the fundamental ideas of Spener; Commentarius historicus et apologeticus de Lutheranismo sive de Reformatione (3 vols., Leipzig, 1692), occasioned by the Jesuit Maimbourg's Histoire du Lutheranisme (Paris, 1680), his most important work, and still indispensable to the historian of the Reformation as a rich storehouse of authentic materials.