In April 1576, David Ungnad was worried. The Holy Roman Emperor Maximilian II had dispatched him to Istanbul in 1573 as his ambassador. Being obedient servants, Ungnad and his colleagues regularly sent detailed dispatches home. At the beginning of April, one such bundle of letters was intercepted and handed to Grand Vizier Sokollu Mehmed Pasha for inspection. Not only was there serious danger that the Ottomans would obtain knowledge of Ungnad’s secrets, in the process, they would also become aware of just how much the ambassador knew about matters which the Ottomans hoped to keep secret from him. For, Ungnad, as part of his job, coordinated a substantial network of spies and informants.

This episode is one of the many fascinating anecdotes recorded in the journal of Stephan Gerlach who served as the Imperial embassy’s chaplain. Educated in Tübingen where he later became professor of theology, Gerlach spent most of the 1570s in Istanbul.

After the Ottomans had obtained the letters written by the Imperial ambassador, discovering their contents was not a simple matter of opening and reading them. As Gerlach emphasizes, Ungnad made heavy use of ciphers and codes to protect his correspondence. Moreover, judging from the letters preserved in Vienna, this particular ambassador was unique in employing invisible ink. After development, the distinctive colour of such writing makes it clearly distinguishable from texts written in regular inks.

While Gerlach’s description of these measures, some exaggeration notwithstanding, is reasonably accurate, his claim that the ciphers were virtually unbreakable is not. The simple alphabetic substitution cipher–in which each letter is replaced by a corresponding symbol–can be broken with sufficient patience and linguistic expertise. In fact, the ciphertexts are sometimes easier to read than the corresponding cleartexts penned by the clerks in Vienna.

Sixteenth-century cryptographical literature–e.g. Johannes Trithemius’s Polygraphiae libri sex (1518) and Giambattista della Porta’s De furtivis Literarum Notis (1563)–discussed more complex ways of making a text unintelligible to unintended audiences. Since early modern European states were notoriously short of the skilled staff necessary to ensure the speedy encryption and decryption of large volumes of official correspondence, the methods they relied on generally remained much simpler. Nevertheless, the ciphers actually used by Venetian diplomats undoubtedly provided greater security than those of the Austrian Habsburgs. As far as invisible inks are concerned, Ungnad relied on lemon juice, which, as Giambattista della Porta’s Magia Naturalis (1568, English translation 1658) makes clear, was one of the simplest methods known at the time. Nevertheless, some of Ungnad’s practices–such as hiding information in otherwise innocent letters–mirrored those employed by Venetian spies in the same period.

Regardless of the question of how sophisticated or simple Habsburg ciphers, codes, and steganographic techniques were, the Ottomans’ apparent failure to exploit Ungnad’s letters in April 1576 had little to do with a lack of ability or even linguistic barriers. For the task of decrypting the letters was given to native speakers of German and Hungarian, all of whom were what contemporaries called “renegades,” men who had converted to Islam and joined the service of the Ottoman sultan.

The most prominent person entrusted with the task was Adam Neuser. Neuser had originally been a preacher in Heidelberg but had sought refuge in the Ottoman Empire when his Unitarian theology and a draft letter to Selim II led to his prosecution for heresy and treason. In Istanbul, he converted to Islam and undertook translation work for the grand vizier. University educated, the man certainly had the intellectual tools to tackle Ungnad’s cipher and he demonstrably possessed cryptological expertise.

However, Neuser worked for the Austrian Habsburgs. When he was given Ungnad’s letters, he falsified translations, secretly allowed incriminating documents to be exchanged, and persuaded his colleagues to abandon their decryption attempts. This time, at least, Ottoman efforts were thwarted because the Austrian Habsburgs had successfully penetrated their ranks.

It is tantalizing that David Ungnad himself nowhere discusses this episode. Perhaps the ambassador preferred to keep it under wraps rather than drawing attention to the value of the Ottomans’ find. The question of the anecdote’s authenticity cannot be resolved from the Viennese records, therefore. It seems clear enough, though, that if the episode had indeed occurred, it caused no noticeable disruption in the information flow between Istanbul and Vienna. Given the pace of the mail as well as the obstacles and dangers which couriers faced during their journeys, a delay of less than two weeks in the arrival of a letter was hardly a cause for concern.

Beyond the question of espionage, counter-espionage, ciphers, and code-breaking, this little story illustrates the ambiguity which Christian Europeans displayed towards those who “reneged.” Ungnad referred to Neuser as the “apostate from Heidelberg,” thereby emphasizing what, in his eyes, was a betrayal of Christianity as much as Christendom. Indeed, conversion to Islam was commonly read as a declaration of loyalty to the sultan. Nonetheless, the diplomat freely admitted to Emperor Maximilian II that Neuser was among his best agents.

From an Ottoman point of view, one might easily infer the lesson that admitting foreigners presents a serious security liability. But for every seemingly disloyal new Muslim there were numerous converts–such as the hero of Lepanto Kılıç Ali Paşa (born Giovanni Dionigi Galeni), the interpreter Mahmud Bey (Sebold von Pibrach), or the “intelligence officer” İbrahim Bey (Pál Márkházy)–whose talents, skills, and knowledge were valuable and whose commitment to the Ottoman Empire was beyond reproach. Most of the time, the benefits outweighed the risks.

In this particular instance, the danger was limited. Yes, the ongoing contest for the throne in Poland-Lithuania had the potential to spark a war which would mobilize the Ottoman army in support of their Transylvanian vassal Stephen Báthory against the rival Habsburg candidate. But then again, the two powerful empires had only just renewed the peace between them and neither party had a particular interest in reviving large-scale military confrontation. Accordingly, the whole affair was swept under the carpet. Doing so was made easier by the fact that, to all appearances, Ungnad’s secrets remained safe.

Featured image credit: Topkapı Palace, Istanbul. Photo by Bjørn Christian Tørrissen. CC BY-SA 3.0 via Wikimedia Commons.