As Long as the King’s Arm?

The​ length of Christ was a spiritual matter in the Middle Ages. Sometimes referred to as the mensura Christi or longitudo Christi, it appeared in manuscripts as a hand-drawn bar or linea, as broad as the width of the page would allow. These lines could be measured by the faithful with a string or ribbon and multiplied so that they might draw the Son of God up to his full height. One manuscript, made in Genoa around 1293, informs the reader that ‘prolonged 12 times this segment shows the height [mensura] of the body of our Lord.’ The resulting measurement had theological significance: it was a means of understanding the enigma of Christ’s Ascension by capturing a trace of his physical presence. It was also practical. The mensura could be kept about the person as a good luck charm – perhaps rolled up in a piece of jewellery – or nailed up inside the house, where it would ward off misfortune. As one manuscript promises, ‘those who wear this measure or keep it in their house or see it every day cannot die of sudden death on that day … And they cannot be harmed by fire or water, nor by the devil, nor by a storm.’

The tradition of the mensura Christi dates back at least to the sixth century ad, when souvenir merchants in Jerusalem sold tapes and ribbons cut to the length of different parts of Christ’s body. Modern concepts of measurement are less personal. Modern metrology officially began in 1793 when the metre was defined as one ten-millionth of the distance from the equator to the north pole. The transition to metric units was designed, in part, to divorce measurement from human affairs. While earlier linear measures such as the cubit and the foot were based on parts of the body (before being standardised, often to the dimensions of the king’s forearm or foot), the savants who planned the metric system under Napoleon wanted to create standards that were ‘à tous les temps, à tous les peuples’. By defining the metre using the dimensions of the Earth, they intended not only to give the unit a basis in something permanent and unchanging, but also to make it accessible to all, re-measurable by any nation on Earth. This was undermined by the fact that the planet’s meridian differs depending on where you measure it – the only ‘correct’ meridian runs through Paris, which annoyed British and American politicians – but the idea of the metre as an arbitrary measure persisted and, in the long run, helped ensure its adoption worldwide.

Since the French Revolution, the metre, along with the six other units of the Système International d’Unités (SI), has been further abstracted and is now defined as ‘the length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second’. In October 2018 the International Bureau of Weights and Measures voted to remove the last physical standard from the metric system, the International Prototype Kilogram, an egg-sized, platinum-iridium mass known as Le Grand K, kept in a sealed vault on the outskirts of Paris. It remains in the vault but is no longer the standard unit of mass. Like other standards derived from artefacts it generated problems. In recent decades, scientists have compared Le Grand K to its supposedly identical témoins, or witness weights, and found that it was losing mass. (Though, technically, as it was the definition of the kilogram, it couldn’t lose weight: the universe could only get heavier.) As of last May, the definition of a kilogram is based on Planck’s constant. Metrologists say that by excising the last physical vestige of the SI, they’ve fulfilled the dream of the savants and finally created an immaterial, universal basis for all metrology. But they have also removed many of the human and mystical aspects of measurement, those dimensions that allowed medieval peasants to believe that a length of ribbon could capture a faint impression of Christ’s salvation.

This journey from a medieval to a modern understanding of measurement is long, complex and muddled. It’s not helped by the fact that a great number of books on the history of measurement take the form of a glossary, listing as many archaic units as possible – ells, bins, stadion, firkins, jiggers, rods, barleycorns, and so on – before referring to Protagoras’ usefully ambiguous ‘man is the measure of all things.’ Emanuele Lugli’s The Making of Measure and the Promise of Sameness avoids this by focusing on premodern understandings of measurement up to the early years of the metric system, and in particular on the period between the 12th and 14th centuries in Northern and Central Italy, where merchants, princes, medieval comunes and the Catholic Church were engaged in a series of power struggles in which metrological definition was an important weapon. ‘Metric discipline emerged as a way to reach consensus in an age of factions and profound cultural differences,’ Lugli writes. ‘It served as the plane of communication between antagonistic and often wildly different parties who spoke foreign languages and thought in codes.’ In this context, units existed as both fallible objects and unimpeachable ideals. Chipped measuring rods and battered capacity containers sparked riots in feudal villages. But they were also supposedly perfect, even holy standards.

Some of the first known units of length were created in Ancient Egypt, where the annual flooding of the Nile swept away field boundaries and made the royal cubit – the length from the pharaoh’s elbow to the tip of his middle finger (c.525 millimetres) – essential to restoring the unquantified quagmire into bounded agricultural land. For the Romans, the division of land did not necessarily involve an understanding of abstract units of measurement, but instead relied on a set of manual operations: a groma (a wooden tool that looks like a four-spoked gallows, with plumb bobs in the place of corpses) to divide land into centuriatio, or square grid. The benefits of this system were ‘hard to overestimate’, according to Lugli. The centuriation allowed the Romans to standardise the layout of military bases, facilitated the collection of taxes, organised the fields that fed the army and were awarded to veterans on retiring. This geometria (‘measuring the earth’) was a practical skill: surveyors walked the land, sighting dividing lines and telling their assistants where to place stakes. But it was also linked to standardised units via the most common historical index of measurement: the human body.

The units used by the Romans, and which they bequeathed to many parts of Western Europe, can be traced back to this anthropometric process, described in the seventh century by Isidore of Seville. In his Etymologiae, Isidore laid out a telescoping set of units starting with the largest units before collapsing each successive measure down onto the human body. ‘Our ancestors,’ he wrote, ‘with great ingenuity, divided the world into parts.’ They put ‘parts into provinces; provinces into regions; regions into districts; districts into territories, territories into fields, fields into centuries, centuries into acres, acres into zones, zones into actus, then rods, paces, steps, cubits, feet, palms, uncia and digits.’ And a digit, he says, is a finger – no more, no less. It’s a wonderfully concise understanding of measurement that shares the medieval desire to encapsulate the universe in a brief schema. But it also avoids the messy (if useful) work of making and maintaining measures; of creating reference standards for traders and merchants and verifying their value. Like so many scholars in the Middle Ages, Isidore seems not to have considered the practical aspects of measurement worthy of attention. And without a meaningful intervention from some sort of central authority, the use of measurement in this period became a byword for dishonesty – confirmed by the various Bible verses that deal with measurement both as a social code and a metaphor for spiritual judgment. From Deuteronomy: ‘Thou shalt not have in thy bag divers weights, a great and a small.’ And Proverbs: ‘A just weight and balance are the Lord’s: all the weights of the bag are his work.’ Measurement is such an obvious vector for sin in the classical and medieval worlds that the first-century historian Flavius Josephus tells us that Cain, after killing his brother, rounded off his bad deeds by becoming the ‘author of measures and weights’ and so ‘changed the world into cunning craftiness’.

Lugli begins his account of standardisation with Fibonacci, who published a number of treatises in the 13th century popularising the work of Indian and Arabic mathematicians. In Liber abaci (1202), Fibonacci explained the use of place value and Hindu-Arabic numerals for the benefit of local merchants (earning him an annual salary of 20 soldi from the masters of the Pisan comune). As an aside, he showed how one might estimate the population growth of rabbits using a formula in which each successive number is the sum of the preceding two – the sequence that now bears his name, though he wasn’t the first to describe it. From his experience in the markets and warehouses of Pisa, Fibonacci saw that there were two types of merchant: ‘Those who measure with their arms, forearms, or steps’ and those who ‘use pertiche or another measurement standard’. He also provides a catalogue of currencies and units in use in various Mediterranean harbours, from Venice to Tunis. Each city employs a different standard, ‘the iugerum, or the aripennio, or the carruca, the tornatura, or the cultura’, and to measure properly one had to distinguish between the ‘quality’ and ‘quantity’ of the standard, as different units are applied to different materials. There is no abstract metre that applies to all standards of length: instead there are units that fit different goods and processes. Fibonacci advises that the difference between 20 braccia of wool and 42 cotton rotuli can be resolved by the ultimate common measure: money (in his case, the Pisan lira). His close attention to measurements and their applications reflects ‘a new cultural awareness’ according to Lugli. ‘I am aware of no other writer who mapped the measurements of the medieval world as extensively as Fibonacci.’ But his observations also demonstrate a tension between ‘idealised notions’ about the human body as a natural source of measure and ‘the political need for certification and control’ that would spur the next developments in metrology.

Fibonnaci’s​ comune salary shows that there was a strong desire on the part of new centres of political power for a process of certification, and Lugli examines a number of cases, including schemes put in place by guilds, city governments and the Church. All were concerned with public displays of measurement. A key example are the pietre di paragone or ‘touchstones’ – Lugli’s term for Italian public standards carved in stone from the 12th century onwards. Carving something in stone has always been a public declaration. In 1173, during a war with the Holy Roman Emperor Frederick Barbarossa, the citizens of Ferrara chiselled their rights into the stone walls of their cathedral for fear of defeat. ‘Stone did preserve them,’ Lugli writes. ‘Ferrara’s are the earliest communal statutes handed down to us.’ Other comunes inscribed moral guidance. In Lucca in 1111, merchants were instructed to ‘commit no theft nor trick nor falsification within the courtyard’. Public statements of this sort eventually encompassed standards of measurement. Sometimes these were metal bars, hammered into the walls of cathedrals, town halls and public squares; sometimes they were carved into the stone itself. Officials charged with upholding standards would insert their handheld measures into these slots, ‘as if they were placing them back in their original moulds’, to verify their length. The carvings were particularly resistant to falsification because of their public location and their durability, and because they couldn’t be shortened, only expanded (an activity that was in any case frustrated by metal endstops). As well as linear measures, some pietre displayed other common units. The pietre in Padua’s Palazzo della Ragione, thought to have been carved in 1277, include standards for roof tiles, bricks, and even a loaf of bread, which appears at waist-height as a circle with a cross through it. Paduans buying their bread could verify its size by holding it up to this mark – a demonstration of the way daily provisions were regulated by the city.

Market inspectors like the sensales of Pisa might have checked their rods against the pietra, but their instruments would often have been bent, warped and chipped. This meant that whenever the sensales were called on to adjudicate, it was the authority of their office that was crucial, not the standard. Anyone caught using substandard measures could be punished in a variety of ways, from fines to public whippings. In Verona’s Piazza delle Erbe, the pietre di paragone are carved into the columns and steps of a small stone canopy set in the middle of the square. Merchants who wielded false measures would be chained inside this capitello during the market’s opening hours, framed by the very standards they had failed to uphold. This is measurement as politics. Lugli writes that such acts made units of measurement ‘sly tools of subjugation’ because each time they are used ‘they slowly turn the world into a place that continues to make sense as long as the power that legitimises the measurements remains in place.’ This can be seen most clearly in the Church’s use of measurement. Throughout the 13th century the clergy in Italy enforced various sumptuary laws, banning plunging necklines for unmarried women and setting maximum lengths for dress trains. Lugli describes the case of a Bolognese woman who was taken to court in 1286 for refusing to have her dress measured during a festival for Saint Dominic. Contemporary documents show that she didn’t object to the restriction per se but to the public verification. This process was repeatedly interrupted by a tumultuous crowd and Francesca refused to continue. Not only could the public certify common standards of measurement: they could also undermine them. Urban life trained people to be shrewd judges: what was the right length of cloth, who bakes a fair-sized loaf. Perhaps this is why traditions such as the mensura Christi were maintained. Lugli writes that, like prayer, measurement is a ‘formula activated through recitation’ and its spiritual power may stem from the fact that it is ‘both a confirmation of touch and a demonstration that contact has been carried out attentively’. In one story recorded in the Golden Legend, a scholar suffering pains in his kidneys and knees took a thread to make a candle of his length, and ‘measured his own height, and then his body, his neck, and his chest’. After each binding and unbinding he calls out the names of Jesus Christ and Saint Dominic, the patron saint of astronomers, and, on reaching his knees, his pain is relieved and he unbinds himself, exclaiming: ‘I am freed!’

Measurement no longer has the same invocatory power, but its reach is far greater. Market inspectors and public rituals of measurement have disappeared: in their place are international agencies that regulate everything from the purity of steel to the size of a pint. Lugli’s book doesn’t cover this world directly, but it describes some of the social and technical shifts that preceded it. Foremost among them is the creation of abstract units, all now defined by constants of nature.