Al-Jazari Combination Lock and the Boxes from Isfahan

“This Ifrit bore me off on my bride night, and put me into a casket and set the casket in a coffer, and to the coffer he affixed seven strong padlocks of steel and deposited me on the deep bottom of the sea that raves…and this wretched Jinni wotteth not [does not know] that destiny may not be averted nor hindered. ”

The Story of King Shahryar and His Brother from The Arabian Nights, translator Sir Richard Burton,1850.


In Category six that consists of “dissimilar designs” al-Jazari describes “A lock for locking a chest using 12 letters of the alphabet”.

Locking board in the alphabet lock, Topkapi manuscript, 1206

Description of the Chest by al-Jazari

The technical explanation, as always, will be colored in blue, so anyone who is not interested in cylinders or cotter-tapered pins can skip those bits. This is a chest with four combination locks in the four corners of the cover. Each combination lock uses sixteen out of twenty-eight letters in the Arabic alphabet; it uses the letters without a diacritical mark, a point, or sign added to a letter to distinguish it from another similar letter. For example, the difference between bāʾ ب (comparable to b in English) and nun ن (comparable to n in English) is the location of the point below or above the letters. Al-Jazari doesn’t explain his choice, perhaps to prevent mistakes.

The four dials

Chest reconstruction from HTTP://WWW.JAZARIMACHINES.COM/EN (link is not working anymore)


The four dials on the chest cover are relatively complex. Each dial consists of three disks with a triangular notch in its outer perimeter. When all the notches were aligned, the chest could be opened. I attached the original drawing of al-Jazari cross-section of the dial with the modern drawing of Hill and added captions:

Integrated drawing of the lock components, the original drawing by al-Jazari, with the modern drawing by the book translator and annotator, Dr. Donald Hill

Since it still seems complicated to comprehend, I added the drawing of the components before assembly:

The dial component, a drawing by the book translator Donald Hill, with my captions

When you turn each of the three cylinders to their proper letter, all notches are aligned and allow the opening of the lock. It requires the knowledge of twelve letters, three letters per each dial multiplied by four dials. This system is held in place together but allows convenient rotation of its components using a cotter-pin. When you want to change the code, you remove the pin and mechanically rotate the disc so the location of the notch will match the chosen letter.

The Isfahan Boxes

None of the wonderful machines of al-Jazari survived the hundreds of years passed, and all we have are beautiful manuscripts. I fantasize about an extensive archaeological excavation in the Palace in Diyarbakir that would reveal remnants of the castle’s clock or any other monumental work. Until then, both boxes with alphabet locks from Isfahan in Iran dated to the late twelfth century are the closest thing to time travel, to see al-Jazari at his work. In the David Museum in Copenhagen, there is a fragmented brass box inlaid with silver and copper with four alphabet locks. The four dials are in a straight line and not in the four corners of a rectangle, but the similarity to al-Jazari’s chest is evident. Like al-Jazari each dial contains 16 letters. The letters which are used are without a diacritical mark. There is a resemblance to the locking process and the details of the mechanism. The box is simpler, and each dial has just two cylinders. Only eight letters (and not twelve) are required to open the crate. On the box there is the maker signature saying:

“Work of Mohammed b. [Ben] Hamid al Asturlabi

 Al Isfhani in the year

Five hundred and ninety-seven [1200 AD]

And I have tested it[it works]”

Fragments of a box made by Asturlabi, 1200 AD, Museum David Copenhagen

To my astonishment there in another safe from the same period by Asturlabi at the Boston art museum. This box also has four alphabet locks of two cylinders, creating eight-letter code. This time also there is an additional three guards’ façade, probably as symbolic protection from a later period. The signature indicates that the box was prepared by Asturlabi four years earlier (593 to AH or 1197 AD). Although it’s childish, I can’t help feeling a bit left out: why two boxes by Asturlabi from Isfahan have survived and not even one machine by al-Jazari? There is no answer, nor there can be one.

Box by Asturlabi,1197 AD, Isfahan, Boston Arts Museum


From the name of the maker, it is obvious that his profession and probably the family profession was producing astrolabes. Astrolabe (ٱلأَسْطُرلاب) is a sophisticated device of astronomers and navigators to measure the angle of a star above the horizon. It has many functions but was used primarily for finding latitude when you know the local time or as a clock when you know your position. There is a good explanation and a demo here. Four astrolabes from the 12th century created by Asturlabi family from Isfahan still exist, but I could not find their pictures. There are pictures of astrolabes from Isfahan from the 9th century until the 16th century, and this is one beautiful example:

The 13th-century astrolabe from Isfahan, Muhammad B.AbiBaker, The Museum of the history of science, Oxford.

Surprisingly, perhaps, there is a link between the astrolabe and the combination locks. The lock consists of rotating cylinders with respect to the alphabet circle. In the astrolabe, there is a framework called “Rete” bearing a projection of the ecliptic plane and several pointers indicating the positions of the brightest stars. This frame is free to rotate in respect to the astrolabe disk, called the mater (mother). Both the astrolabe and the alphabet lock are rotating mechanical systems around the center. This is done in both cases by using a cotter pin (a tapered pin) that holds all the components in place and allows rotation around an axis. This pin has the shape of a horse head, hence his name in Arabic فرس (mare). I attach a photo of astrolabe dismantled; you can see exactly the same mechanism and the same cotter pin (red circle) as in the drawing by al-Jazari above.

Astrolabe dismantled for parts. The cotter pin in the red circle

If you really want to go on a historic-scientific journey, you can read the guide that Geoffrey Chaucer wrote for his 10-year-old son Lewis. Chaucer, one of the fathers of the English literature and the author of “The Canterbury Tales” was also an astronomer. This is the first publication in English on this topic as well as a great introduction to the Astronomy in the 14th century. The guide contains more than fourty (!) uses the astrolabe.

Who’s ahead?

Al-Jazari wrote  in the opening paragraph:

“The earlier [workers] in this craft made locks for locking and opening by means of the letters. Among them were [those that] locked by means of  four  a chest and made a lock on its lid as I shall describe”

Al-Jazari, obviously, did not claim primacy. Is it possible that the Isfahan boxes are part of the boxes that al-Jasari mentioned? Could it be that al-Jazari book got to Isfahan and inspired Asturlabi to build his boxes? The answer is probably no to both. The boxes were made in the years 1197-1200. We don’t have an exact date for completion of the book.  Rachel Ward claims that the book was written between 1200 to 1197. It’s a little earlier than Donald Hill who believed that the book was written between 1204-1206. The small gap is due to different sources. Hill was relying mainly on the copy from Oxford University, and Ward is basing her calculation on the earlier copy of Topkapi. Either way, the closeness between the time the book was written and the dates of the production of the boxes in Isfahan almost negates the possibility of mutual influence. Much more likely is both the Isfahan boxes and al-Jazari’s chest are part of the same rich material culture in the Muslim world at the time.

It is interesting to note that the first alphabet lock in Europe is probably the work of Giovanni Fontana, A Venetian engineer from the 15th century, three hundred years after al-Jazari. Fontana was very diverse, including measuring heights with falling stones, water and sand clocks, and trigonometric measurements. He wrote one of the first technology books in the Renaissance: “Bellicorum Instrumentorum Liber.” The book includes siege machines but also fantastic inventions like a bird propelled by a rocket, and an early version of four wheels bicycles and last but not least an alphabet lock:

The alphabet lock of Giovanni Fontana, 1420-1430

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