Thread by @AndrewBrunatti

The Stallburg in Vienna.

An elegant 16th Century building on the edge of the sprawling Hofburg palace. It housed the royal art collection and the royal stables.

It was also home to Austria's most efficient intelligence organization.

A 🧵

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The late-Renaissance building with an inner courtyard surrounded by arcades was multi-functional: it housed the royal stables, guest apartments, the royal art collection, and an armoury. In fact, the ground floor is still used as the stables for the vaunted Lipizzaner Stallions.

Around 1711 the Stallburg also became the home of the Ziffernkanzlei--the 'Number Office.'

A name both suggestive and vague (and one of many used throughout the organization's existence), it was really the secret office for mail interception and decryption.

The collection of the Albertina Museum contains several architectural surveys of the Stallburg, which we can use to piece together an image of this multi-functional building.

The drawings here date from 1773, and show the ground floor dimensions for the stables.

The 1st floor was mainly used as guest apartments until the 1740s, but a renovation in 1745 moved the War Chancellery onto the floor.

In this plan dating from 1745, the floor is labelled 'Chancellerie de Guerre', but still shows some rooms labelled as dining rooms and a chapel.

The 2nd floor was predominantly used to showcase the royal art collection, but one section in the N/W containing an armoury was vacated for 'offices' in 1750. This section of the 2nd floor is most likely where the Ziffernkanzlei became permanently located.

Plan from c1820-1845

This would also fit with the fact that when the royal art collection moved out of the 2nd floor of the Stallburg in the 1770s, it's known that the Ziffernkanzlei expanded into some of the vacated rooms (the office grew from 9 employees in 1737 to 23 by 1780).

And when I say 'efficient'...

Different sources indicate that the Office would take delivery of 4-5 batches of letter bags full of intercepted letters per day. The letters were sorted, and those of interest were unsealed, copied precisely, and re-sealed.

The letter bags were loaded back onto mail coaches for regular delivery, all within 3-5 hrs for each batch of letters. The nighttime batch would start at 7pm, be done by between 11pm-1am. Reporting from intercepted letters could land on the Emperor's desk by 7am the next morning.

Some might say that the employees of the Ziffernkanzlei drew the short straw, being relegated to one of the oldest buildings in the Hofburg complex above the horse stables.

But the Stallburg also offered some interesting operational benefits.

Having the ground floor designed as a stable--designed for lots of horse traffic--meant that the courtyard was large with large corridors. There was plenty of room for mail coaches diverting into the Stallburg through the day, and for loading/unloading directly from the building.

Also, the late-Renaissance design was modelled on Italian palazzos that were often fully enclosed with one main point of entry/exit. This meant the courtyard and interior of the Stallburg was blocked from public view--probably handy when clandestinely unloading letter bags.