# Turning grille cipher > Letters rearranged through a rotating mask - Date: c. 1745 - Era: Industrial age - Domain: [Writing & Communication](https://lastcodex.org/en/domains/communication/) - Rebuild stage: III (Crafts & cities) - Difficulty: 1/5 - URL: https://lastcodex.org/en/inventions/turning-grille-cipher/ A turning grille distributes a message’s letters through openings in a mask. Each quarter-turn reveals new cells; the resulting transposition can be undone with the same grille. ![Turning grille cipher · Letters rearranged through a rotating mask](https://lastcodex.org/_astro/plate.BVbjfUZV_gtuVh.webp) ## Legend 1. Square mask of stiff paper 2. Cut-out windows 3. Stationary gridded sheet 4. Orientation mark on the mask ## What it is A turning grille is a mask pierced with windows that determines where the letters of a message are placed. It rests on a sheet with the same grid and rotates to expose other cells. The recipient needs an identical pattern of windows and must know the starting position, direction of rotation and reading order. The letters themselves stay the same; their positions change. This is a transposition cipher. The mask and sheet form a lightweight manual device. Squared paper can provide both the writing surface and the material for the grille. Stiffer paper is easier to handle repeatedly, provided it stays flat. A Cardan grille has a different use: a message is written through its openings, then harmless text fills the gaps to conceal its presence. A turning grille uses successive positions to distribute the message within a block of letters. ## How it works ![A cut-out mask with four windows and an orientation mark, propped above a blank gridded sheet on a desk, with an inkwell and a quill beside them](https://lastcodex.org/_astro/v1.CsnfcrtT_2pL2s1.webp) _The windows expose only the cells to be filled._ Place the mask on the sheet with its orientation mark at the top. Write through the windows from left to right, working down the rows of the sheet. Once the visible cells are full, lift the mask, turn it a quarter-turn clockwise and replace it over the same square. The sheet stays still. Continue the message through the newly exposed windows, always following the sheet’s rows rather than the mask’s changing orientation. A demonstration on a square four cells wide uses four windows. Numbering rows from top to bottom and columns from left to right, their initial positions are (1,1), (2,2), (2,4) and (4,2). Each of the four orientations exposes four different cells; together they cover all sixteen without overlap. For this to work, each window must belong to a different set of positions connected by quarter-turns. Two windows in the same set would expose cells already used. With this grille, BONJOURMONVOISIN becomes BIOOUORNNSVINJMO when the mask is removed and the square is read row by row. The recipient writes that string into an empty square, row by row, then reads only the windows in the same orientations and order used by the sender. This recovers exactly BONJOURMONVOISIN. A shorter message can be padded with extra letters, provided both parties agree how to identify its end. An orientation error is enough to scramble the recovered message. ## How to do it ![Two windows cut side by side on a diagonal in stiff paper, with a narrow strip of paper left between their nearest corners, on a wooden board beside a folding knife and shavings](https://lastcodex.org/_astro/v2.CANh2ZoF_6wGAo.webp) _The paper between the windows keeps the mask in one piece._ Draw a square divided into four rows and four columns on stiff paper, then reproduce exactly the same grid on the writing sheet. Make the cells wide enough to hold a letter comfortably. Cut windows at (1,1), (2,2), (2,4) and (4,2), leaving a paper border around each opening. These borders stop the openings from joining up and keep the central parts attached. Leave an outer margin as well, so that the mask can be held without covering its windows. Put a small distinctive mark at the middle of the top edge. It turns with the mask, moving from top to right, bottom and left. This indicates the current position without turning the mask over. Cut on a protected surface and keep fingers away from the blade’s path. An adult should make the cuts for children. Move the mask by hand; it needs no axle or fastening. Before writing a message, try the grille on a spare sheet. Mark the cells exposed in each orientation with a different colour. No cell should be marked twice, and none should remain empty. If a window lands on an earlier mark, correct the design before cutting another mask. For several message blocks, return to the agreed starting orientation each time. ## History and evolution In a 1995 study, Karl de Leeuw and Hans van der Meer identified a letter in the archives of William V of Orange as a turning-grille message. After deciphering it, they attributed it to Carl Anton König and to the correspondence of William IV. The letter mentions French troops passing through Camberg. By comparing these clues with archives and the military chronology, the two researchers dated it to April 1745, a date they consider highly probable. On their dating, the letter is older than the printed descriptions of the method. ![A square sheet ruled into four rows of four cells, each cell washed in one of four colours, ochre, green, red or blue, with four cells of each colour spread over the grid, and a palette, a glass of water and a brush beside it](https://lastcodex.org/_astro/v3.8rFKFQ5L_Z2b6sRX.webp) _One colour for each position of the grille: every cell is marked once, none twice._ In the late eighteenth century, Carl Friedrich Hindenburg studied turning grilles and the constraints that prevent their windows from overlapping after rotation. In 1881, Edouard Fleissner von Wostrowitz described the method in his manual of military cryptography. Among his proposals was the addition of meaningless columns of letters to hide the centre of rotation. The Dutch army adopted a variant in 1885. During an exercise in 1913, Captain Van der Harst deciphered a message prepared this way. Predictable words and the mask’s geometric constraints helped his search. The American manual Basic Cryptography still described the paper grille in 1950, while stressing its security limitations. Today the method is useful for studying transpositions and solving cipher puzzles. It does not provide suitable protection for modern confidential communications. ## Key facts - Principle: Transposition of letters - Movement: Successive quarter-turns - Early evidence: Letter dated April 1745 by De Leeuw and Van der Meer - Material: Paper with cut-out openings ## Requires - [Paper](https://lastcodex.org/en/inventions/paper/): A cheap surface for memory (c. 150 BCE) - [Writing](https://lastcodex.org/en/inventions/writing/): Knowledge that outlives memory (c. 3,300 BCE) ## Sources - [A Turning Grille from the Ancestral Castle of the Dutch Stadtholders](https://staff.science.uva.nl/h.vandermeer/pubs/koenig.pdf), Karl de Leeuw et Hans van der Meer, Cryptologia (1995), copie University of Amsterdam - [The Solving of a Fleissner Grille during an Exercise by the Royal Netherlands Army in 1913](https://ep.liu.se/ecp/149/012/ecp18149012.pdf), Karl de Leeuw, HistoCrypt 2018, Linköping University Electronic Press - [Basic Cryptography, TM 32-220, avril 1950, §31b](https://www.nsa.gov/portals/75/documents/news-features/declassified-documents/friedman-documents/publications/FOLDER_238/41748889078809.pdf), Department of the Army, exemplaire déclassifié conservé par la National Security Agency Fact-checked on 2026-10-17. --- The Last Codex · https://lastcodex.org/en/inventions/turning-grille-cipher/ · © The Last Codex. 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