The Site of the Cross

On December 14, 2016, Searcher, on the forum, suggested that the cross-shaped item in the hand of a nymph on folio 79v might be a cross-staff. This was an intriguing idea, especially considering the way in which the instrument is held and the fact that there is another nymph holding something that looks like calipers, so I looked up some of the history of cross-staffs to see if there might be support for the idea.

The cross-staff is an ancient instrument which may trace back as far as the Chaldeans, who are also connected to early forms of astrology. In the Renaissance, it was used in navigation, but its original purpose was to study and measure distances related to the sun and stars. The staff provided a way to guide the eye and was the forerunner to instruments such as the quadrant and sextant.


In its simplest form, the cross-staff consists of a rod with a smaller crossbar mounted at 90 degrees to the longer bar. The smaller bar is known as a “vane” or “transom”.

A cross-staff was held to the eye so the person using it could site along a line to the sun and compare this with the distance to the horizon. The vane was adjusted back and forth until both could be brought into view at the same time. Refinements included various means to move the crossbar, and markings on the instrument, in degrees and minutes, to help determine distance. Sometimes multiple vanes were added, but the basic instrument needed only one.

The cross-staff was sometimes known as Jacob’s staff. This may be based on the ladder Jacob envisioned stretching in a line from Earth to heaven. It has also been suggested that the name comes from one of the medieval names for the constellation we know as Orion, which has a short “belt” of stars resembling the vane on a cross-staff.

In French, it was called arbalete, rayon astronomique, and baton de Jacob, or arbalestrille for the marine version (the fore-staff). In Portguese, balestilha. In Latin, radius astronomicus, and in German, Jacobs-Stab or Stab und Kreuz, or just Kreuz.

Three modes for using the cross-staff for siting and measuring are illustrated in Gemmae Frisii de radio astronomico et geometrico liber (Frisius, et al, Cavellat, 1557).

The earliest reference to the cross-staff, so far identified, is from 11th-century China. In Europe, the earliest references to modern use of the instrument are from Provençe in the 14th century. Of particular interest is a reference by Gersonides, a Jewish scholar who believed in astrology, who describes the instrument and attributes its uses not only to measuring distances between celestial bodies, but also their diameters.

In this image, Moslem astronomers discuss the use of the astrolabe (upper right) and another uses a double sighting rod (left) while an early form of quadrant sits next to him on the table. The Q’uran (written in the 7th century) includes a passage about Allah/God having set out the stars to help navigation at night, thus inspiring an interest in the practical application of astronomy. [Image courtesy of the University of North Florida]

By the 19th century, a modified cross-staff with a round or square head, and sometimes a quadrant of slits, was used in surveying, in combination with a rod or chain and a number of staves. It was useful for measuring fields, platting lands, and certain forms of cartography.

The Cross-Staff for Navigation

Yemeni Astrolabe, 1291 [Courtesy of the Metropolitan Museum of Art: Edward C. Moore Collection]

Of particular interest to Voynich researchers is the history of the cross-staff for navigation on water. In marine navigation, it was known as a fore-staff, so-called because the person using it faced the direction being observed, in contrast with the back-staff which was used with one’s back turned. Adjustments had to be made for how high the person was above the water.

It may seem surprising, but historians claim that the cross-staff was not used for marine navigation until fairly late in the middle ages.

In the Mariner’s Museum, they have this to say about the history of the cross-staff:

“…sailors did not use it until the early 1500s; the first recorded date was 1514. As with other early navigation instruments, the first use for the Cross-Staff was in astrology, in measuring the altitude of stars to help forecast the future.”

William Wales notes, in 1744, that John Werner, of Nuremburg, recommended the use of the cross-staff as a marine instrument for determining longitude, by observing the distance between the moon and stars, in a book printed in 1514 (W. Wales, 1777), which is likely the same reference noted by the Mariner’s Museum.

In Motorboating (July, 1947), there is a practical description of the difficulties of using an instrument like a cross-staff on the sea:

“The pitching, rolling deck of a ship prevented general adaptation of the astrolabe. The cross-staff required the observer not only to sight directly on the blazing sun but also to look at two things simultaneously: the sun and the horizon. In the middle and high latitudes this latter job was not too difficult. In the low latitudes traversed by so many ships of the early days, it was nearly a physical impossibility to sight on a noon-day sun nearly overhead and a horizon dead ahead. These disadvantages led John Davis to invent, in 1590, his Back-Staff or Sea-Quadrant.”

Andrew MacKay, in 1793, sheds further light on why the cross-staff was not the instrument of choice for determining distance on water in the early days:

“The method of reckoning the latitude in degrees and minutes being introduced, instruments for observing altitudes were divided accordingly.– The Astrolabe, (a circular ring, having a moveable index and fights,) was applied to observe altitudes at sea. It was, however, supplanted by the Cross Staff, and that again by the Quadrants of Davis and Hadley, in succession.”

Thus, he suggests that use of the astrolabe preceded the cross-staff for marine purposes, with the quadrant eventually succeeding it.

On the left is a sighting rod (without crossbar), to the right, an astrolabe, constructed of overlapping, rotating rings—an instrument commonly used in navigation. Note the cloud band and the pattern in the background. [British Library, Bodley Digby 46, late 1300s]


If the object in the hand of the nymph on folio 79v is a cross-staff, then it’s unlikely that it’s intended as a marine navigation instrument—the astrolabe and other means were more commonly used for this purpose before the 16th century. In the early 15th century, the cross-staff was primarily used for land navigation, architectural measurement, and astrology.

Unfortunately, the other images on the page, below the cross-wielding nymph, add little to our understanding of the cross-shaped object unless, perhaps, the Jacob’s Ladder story is being used in a metaphorical way and the presence of a nebuly-like “umbrella” over the nymph and her crow’s-next viewpoint are pointing to a path to heaven, a concept particularly prevalent in Christian iconography, but common to many cultures.

Or perhaps it’s the astrological significance of the cross-staff that is alluded to in the Voynich manuscript. If the various nymphs are personifications of constellations, as suggested by Koen Gheuens, it would not be out of place to find a cross-staff aimed at the stars or a possible connection with Jacob’s rod, which was traditionally associated with Orion’s belt.


J.K. Petersen

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7 thoughts on “The Site of the Cross

  1. D.N. O'Donovan

    -JKP – Though I cannot now find any reference to this suggestion before my post of May 12th 2010 ( which was recently republished at voynichimagery in relation to another issue), I am sure that the same suggestion – and possibly one supported by a body of evidence and argument – was around before I began investigating the manuscript.

    The very odd policy endorsed by prominent figures on Santacoloma’s second mailing list was to deny information about precedents on the basis that accurate attribution was ‘unnecessary’ – a very peculiar position, but there you are. I was never able to track, read and evaluate the original and do not know if it was a bit of kite-flying or the conclusion of carefully documented and reasoned investigation. If anyone is able to find mention of this earlier than 2010, I’d be very grateful indeed for the information.

    The reprint of that earlier post:

    As I keep emphasising, the reason that scholars insist on accurately attributing the source of one’s information is not only to avoid the merest hint that one is so intellectually bankrupt as to plagiarise, but so that one can avoid wasting time endlessly re-covering old ground, when there is still so much yet to be done.

    1. J.K. Petersen Post author

      Diane, I just read the post that you linked, from 2010 (this is the first time I’ve seen it) and it talks mainly about how the VMS differs from Christian imagery. It does not include any information on the history of the cross-staff.

      I don’t see how my blog is re-covering old ground unless another Voynich researcher has posted a detailed look into cross-staff history and, in particular, has pointed out that the cross-staff was not used for marine navigation until the 16th century.

      Searcher’s suggestion was put forward at the time we were looking at all the possible uses for the various VMS tools (e.g., tongs/calipers, etc.) and was a natural evolution of that conversation.

      I had two motivations for blogging about this device:

      1) because I discovered that the cross-staff was primarily a land-navigation and architectural instrument, not a marine navigation instrument, in the 15th century, a point that is important in understanding the cultural climate of the time, and the possible interpretation of the device, and

      2) because I felt it was important to emphasize its connection to astrology, including the linguistic connection to the constellation Orion, an interesting fact that might support some of the original work K. Gheuens has been doing on allegorical interpretations of the nymphs in relation to stars. Since you did not mention Orion in your blog, I don’t see this as covering old ground, either. It simply adds to the list of possible interpretations.

      This is where I stand on the subject of precedence… You mentioned in your blog that the cross in the VMS could “represent any one of a hundred things” and provide a list of possibilities, but you did not expand upon the idea of Jacob’s rod. Mentioning an idea in a list of possibilities without describing its connection or significance is not sufficient to claim precedence.

      I liked Searcher’s idea that the object might be an instrument and thought it worth looking into the subject more fully, but whether it is a cross-staff is still very much up to debate. It’s the wrong size and it’s being held the wrong way. Why fight to claim precedence for an idea that is still highly speculative? I prefer to use my time and energy to unearth clues that answer the question one way or the other rather than worrying about the many people who make unsubstantiated passing references. I am quite happy to cite substantive precedents.

      I don’t know what the cross-like object represents, and maybe never will, but I did discover that if it is a cross-staff, in the early 15th century it was used on stable ground rather than bouncing boats and was intrinsically better for sighting the horizon in northern climates than those that are closer to the equator.

  2. Koen Gheuens

    I hadn’t studied the particular use of these cruciform tools yet, so this is a nice read.

    Now, to be perfectly clear, in my recent post about this object I did not require the device to be used for navigation. I think it is shown the way it is to bring to mind the stern of a ship from which a small sail points outward. The whirlpool behind the nymph is to be read as a triangular main sail. The front part of the ship is missing because Argo Navis was only the back half.

    In other words, there are allusions to ship parts because this particular constellation is a ship. Your use of the term crow’s nest was surely a subconscious result of that 😉

    1. J.K. Petersen Post author

      The cross-staff was certainly known to mariners, even if the astrolabe was the instrument of choice for on-sea measurements before the 16th century. Cross-staffs were probably carried on sea journeys that emphasized exploration.

      Exploratory journeys often included a botanist and cartographer and the cartographer would likely have had a sighting rod or cross-staff in his tool kit. Once they made landfall, a cross-staff could be used on firm ground by mariners or, if they were along for the journey, by astronomers and cartographers.

  3. voynichbombe

    The cross-staff as measurement device was already known to the egyptians. The tip that makes it resemble a christian cross is actually unnecessary, the T-form suffices. What’s essential is the plumb-line. There is a certain author trying to establish the celtic cross staff as a more precise instrument for astronomical measurements, which seems striking, but has little factual evidence surrounding it.
    If you use the staff in “secondo modo” (upright), you can work with the shadows, no need to subject your eyes to blazing sunlight. But of course it can also be used at night with the moon.
    As a naval device it seems unfit and also unnecessary, a modern “gimmick” like the “viking sunstone”. If the sea is quiet enough, one can use the mast for a similar purpose.. the coarse approximation possible like this also sufficed most navigation purposes, as we know. And the seafarers had other means.. color, taste.. experience. It is perfectly possible to sail Greenland => Newfoundland in a fourtnight, without compass or the like. It has been done.
    I do not claim precedence on the aforementioned findings, because they were found by means of surfing the web, and it seems highly unlikely that I was the first person to lay eyes on the found information, unless the respective website creators were blind.

  4. VViews

    Great post, JKP!
    Reading up on this, I found a note in Freudenthal’s Studies on Gersonides, p. 342, note 71 which may be of interest. [my translation]
    “Gersonides calls this instrument megalle amuqot, “revealer of depth”. This denomination can be understood as deliberately carrying a double meaning, evoking both profound truths and depth in the mathematical sense, which is the relative height of one star to another”.
    In the same volume, an essay by Mancha mentions on p. 22 that Jacob’s Staff was also named by Peter of Alexandria in his latin translations as the Revelatore Secretorum… the revealer of secrets.
    This leads me wonder if this instrument might be depicted here, not as a literal illustration of astronomical subject matter in the text, but as an allusion to the text as a place where deep secrets are revealed.


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