How tall was Jesus? Or, measurement and the making of the modern world.

The mensura Christi provides insights into the making of modern measurement—and how the history of metrology created our modern world, subdivided into arbitrary units that define and shape our lives.

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Measurement is one of life’s invisible forces, an arbitrary mechanism humans have created for dividing the world into parts, so that we can more easily control it. Our systems for quantification and classification are so ubiquitous that we forget they are constructed by us, often through historical accidents, and that the solidity we attach to these measures is merely an agreed-upon mirage.

One clue that our methods for subdividing our world are more arbitrary than we might imagine comes from this fact: until 2019, a kilogram was no abstract concept, but a physical object in France made out of a platinum alloy.

Known as “Le Grand K,” it is kept in a secure vault below Sèvres, Paris, tightly sealed under three bell jars, each locked. For extra security, only two of the keys are kept in France. Every so often, Le Grand K is taken, with ceremonial awe, from under the bell jars for a ritualized weighing.

For reasons not fully understood, the object has, over time, lost a tiny amount of weight, about 50 micrograms—roughly the same weight as one eyelash. That doesn’t mean the kilogram has become lighter. Instead, as James Vincent points out, because the physical object beneath those locked bell jars is “the definition of the kilogram, it can’t technically lose or gain weight. Instead, it’s more accurate to say that the rest of the world has been getting slightly heavier.”

To avoid the world getting heavier relative to a standard embodied by a modestly decaying object, Le Grand K was retired in 2019. Now, a kilogram has lost its romance. It can now be defined as “the mass of a body at rest whose equivalent energy equals the energy of a collection of photons whose frequencies sum to [1.356392489652×10⁵⁰] hertz.”

We like to pretend that measurement classifies the world, slapping objective values onto reality. But what we often forget is that, in so many ways, measurement creates our world, changing the meaning of how we experience reality, and in the process, shaping so much of modernity that we take for granted.

Measurement is also part of what makes us human. No other species is capable of using abstractions to subdivide the world. Doing so has also allowed us to partition the interconnected wholeness of existence into more manageable, discrete parts. And that has allowed us to control an ever-larger slice of our existence.

The question, though, is this: have we gone too far?

How Tall Was Jesus?

In medieval Florence, a holy manuscript was illustrated with an exactly measured blood-red line. The dye on the page gave an extraordinary power: to conjure Christ into being, allowing a special communion with a physical manifestation of the divine. The text instructed the reader to use a string cut exactly to the size of the blood-red line. Multiply that string to feel the presence of Jesus, it said, for “prolonged 12 times this segment shows the height [mensura] of the body of our Lord.”

According to the historian Emanuele Lugli, these subdivisions of Jesus’s body, known as mensura Christi or longitudo Christi, were not merely curiosities to understand how tall Jesus was in his earthly life. Instead, they were said to confer divine protection, as the act of physically measuring out Christ’s length would summon his spirit, warding off evil and calamity. “Those who wear this measure or keep it in their houses or see it every day cannot die of sudden death on that day,” one manuscript explains. “And they cannot be harmed by fire or water, nor by the devil, nor by a storm. And the pregnant woman who wears it cannot die of childbirth.”

This manuscript built on a tradition of relics, which sometimes derived their spiritual power from physical measurements. As Lugli notes, “Sellers of tapes and ropes cut to the size of Christ’s body parts are recorded in Jerusalem since the sixth century.” There were lengths cut to match his footprints and reproductions that measured the imprints of his fingerprints on the column of the Flagellation. There were even subdivisions of Jesus’s body’s length made so small that they could be worn as jewellery, allowing one to wear the physical presence of the divine, broken into carefully measured parts.

If these measurements are accurate, Jesus was about 6 feet tall (1.82 m). (Many modern scholars believe it’s more likely that he was around 5 foot 5 inches tall (1.68m)).

While the mensura Christi had immediate instrumental value—it was said to save you from fire, water, the devil and storms—it also reflected a worldview that would grow through the Scientific Revolution and the Enlightenment. Measurement, in this conception, was the antithesis of evil, because it gave concrete form and structure to the world, whereas the devil was an agent of immaterial chaos.

A medieval manuscript housed at Cambridge University puts it bluntly: “Everything which exists is not without some form. But where there is form there is necessarily measure, and measure is something good. Absolute evil, therefore, has no measure, for it lacks all good whatsoever.” This viewpoint considerably shaped the evolution of human history.

Measurement in the Ancient and Medieval World

In the distant past, measurement had a centrality to life that seems so banal to us that we rarely consider it in modernity. But in the past, accurate measurement was not just the key to technological revolutions, it was also a life or death matter for millions who were scraping to survive in a much harsher world.

The first known attempt to standardize measurement dates to 2900 BC with the building of the Khufu Pyramid in ancient Egypt. A block of granite was cut, matched to the length of the pharaoh’s forearm and hand. It was known as the Royal Egyptian Cubit, and royal decree ensured that every wooden cubit used in the kingdom was to be measured against “the granite cubit every full moon, failure to do so was punishable by death.”

The threat seemed to have worked, for no length of the pyramid’s base deviates from any other by more than 0.05%, an extraordinary level of precision for a building completed nearly 5,000 years ago.

The ancients also saw measurement as a way to unlock the power of numbers, which were to be mathematical representations of divine proportions. As James Vincent notes in his book Beyond Measure, Plato proclaimed that the ideal number of residents of a city was 5,040 because that’s what you get when you multiply 7 x 6 x 5 x 4 x 3 x 2 x 1. The purity of the measurement gave it spiritual authority.

But for thousands of years, despite a widespread sense that pristine measurement could unlock hidden power, few measures followed such elegant, standardized simplicity. Instead, medieval measurement became a tool of oppression. As Vincent points out, this was particularly acute with “the grain measure.” Shaking dry goods, heaping them, or leveling them could yield drastically different amounts—sometimes adding or subtracting as much as a third from the total amount being measured.

The grain you get from your farm is needed not only to feed your family, but also to pay your feudal dues and barter for goods at the market. When you take it to be sold, you are watching someone measure out not only months of labor, but, potentially, the future of your family. In lean years, shaking or striking the container to let the seeds settle could be the difference between survival and starvation.

A lack of standardization could even shake kingdoms, as was the case with the signing of the Magna Carta in 1215, which constrained King John’s power. As Vincent notes, one of royal concessions was a guarantee that there would be “but one measure of wine throughout our whole realm, and one measure of ale and one measure of corn.”

Beyond provoking backlash, kings also became acutely aware that differing standards of measurement could prove catastrophic, even for their top priorities.

Christopher Columbus, for example, wrongly concluded he had reached Asia when he arrived in the Bahamas because he was using the estimated circumference of the Earth based on a calculation done “by the medieval Persian geographer, Abu al Abbas Ahmad ibn Muhammad ibn Kathir al-Farghani (a.k.a. Alfraganus)” but wrongly believed that Alfraganus had been conveying distance using Roman miles (4,856 feet), when he had been using Arabic miles (7,091 feet). With other measurement errors, Columbus concluded that the Earth was a quarter smaller than it actually was.

Or, take, for example, the Swedish warship the Vasa, which was to be the flagship of King Gustavus Adolphus’s fleet. Built between 1626 and 1628, no expense was spared, but it faced a problem that money couldn’t solve: non-standardized measurement.

Some of the builders were using rulers that measured a foot in the Swedish way, which was 12 inches. The others were using Amsterdam feet, which had but 11 inches. The timbers were mismatched, and when coupled with a flawed, top-heavy design, the Vasa made it less than a mile into her maiden voyage before toppling over and sinking. (The king’s advisers had been afraid to raise their concerns with him, so important warnings went unsaid before the comically doomed sailing, an early instance of what I call “the dictator trap”).

From Columbus to the Vasa, there was plenty of evidence: it was time to standardize how we subdivide reality.

Measuring the Measurements

Modern metrology—the scientific study of measurement—highlights the need to define measures; to implement them in practice; and to ensure traceability, which is the ability to verify relative to a standardized reference, whether a measurement has been accurately made.

There have been many units of measure mostly retired over human history precisely because they failed to provide traceability and therefore guaranteed confusion. For example:

• Furlong (the distance an ox could plow without resting)

• Ald (a Mongolian measurement of the distance of a man’s outstretched arms)

• Sana lamjel (the distance from the floor to the top of the fingertips of the king—Nongda Lairen Pakhangpa—when he raised his hand above his head)

• Butt (a measure of liquid volume equal to two hogsheads—obviously—or somewhere between 450 and 1,060 liters)

• Hobbit (not the hairy-footed variety, but a Welsh measure of volume/weight).

The biggest leap forward in modern metrology, which aimed to destroy such arbitrary metrics, emerged after Louis XVI was decapitated. On the eve of the French Revolution, the historian Ken Alder notes, there were 800 different names for measurements used in France, but in practice, these 800 terms represented 250,000 different standards. Killing the king and overthrowing his oppression meant uprooting the old ways. Central to that was also decapitating the broken royal system of measurement, from calendars to clocks and weights to lengths.

A decimal craze swept across France, where it was deemed right and proper to subdivide everything by ten. From 1793 to 1805, France replaced its calendar with a decimalized one—similar to a model used in ancient Egypt—in which months were subdivided into three weeks, each ten days long, a duration known as a décade. Days were broken down into ten hours, comprised of 100 minutes, with each minute divided into 100 seconds. To correspond to the Earth’s rotation, this meant that an hour was—in our terms—144 conventional minutes long and minutes were comprised of 86.4, instead of 60, conventional seconds.

There were also momentous scientific efforts unleashed to try to create more objective and pristine measures, including the expedition that provides the origin story of the meter. The calculation was to be based on one ten-millionth of the distance between the North Pole and the Equator through Paris. Two scientists spent six years on the project. When they triumphantly returned with their calculated length, it was enshrined in a length of pure platinum, a measure we still use today.

But in the ultimate illustration of the fallibility and arbitrary nature of measurement, the two scientists made a small miscalculation, such that the meter—to this day—is 0.2 millimeters shorter than it should be. One of the scientists, Pierre-François-André Méchain, went mad with despair when he realized his mistake. In his crushing depression, he took off on an expedition in the hopes that he would cheer up. Instead, he got bitten by a mosquito, contracted malaria, and expired, taking his shameful secret of miscalculation with him to the grave. (It has recently been rediscovered).

Their calculation error has been perpetuated in every subsequent definition of the meter, including its more apparently objective standard definition. Since 1983, the meter has been defined as “the length of the path traveled by light in a vacuum during a time interval of 1/299,792,458 seconds.”

It is a strange fact that Usain Bolt is famous for quickly running 1/100,000th of the distance between the North Pole and the Equator—passing through Paris—but due to measurement error, Bolt set his speed records based on a lie: a distance not of 100 meters, but of 99.98 true meters.

John Graunt, Gunter’s Chain, and the Origins of Modern States

In 1662, John Graunt, a self-educated London hat maker, gave birth to modern population statistics by analyzing the city’s “Bills of Mortality” and quantifying various causes of death. This, as Kat Eschner notes, was arguably the founding systematic use of “Big Data” to make sense of our world—so that we could better control it. By analyzing causes and locations of death, people were better prepared to avoid outbreaks, including plague, which would ravish the city in 1665, three years after Graunt first published his statistical analyses.

The development of statistical demography gave birth to a new form of state power, in which governments were able to measure their populations—and better control them. As Ian Hacking describes in The Taming of Chance, the ability to accurately measure gave rise to bureaucratic dominance, in which states used counting and statistical measurements to impose their will on the populous, as illustrated rather unfortunately with the Down Survey of Ireland in 1679.

Three decades earlier, Oliver Cromwell’s “New Model Army” had occupied Ireland after a rebellion, and the re-conquest was funded by land guarantees: investors were to be given 2,500,000 acres of Irish land upon the completion of the military campaign. To pay out, the government needed to measure Ireland—and precisely. The resulting survey—the first national land survey anywhere in the world—gave the occupying force the ability to accurately confiscate land. The man who conducted the survey, William Petty, demonstrated how measurement could lead to power, as he ended up with most of the land which now forms County Kerry in southwest Ireland.

To parcel up Ireland, the survey used a Gunter’s Chain, a 17th century literal chain of 100 links, that was used to measure land distances. Each link was 7.92 inches long, which made the entire chain 22 yards, or 20.1 meters long. This may seem esoteric, but it has almost certainly quite literally shaped your life—particularly if you live in the UK or one of its many former colonies, including the United States.

In 1785, Thomas Jefferson convinced the fledgling American state to adopt a grid system for surveying and subdividing its land. To measure the vast nation, a Gunter’s Chain was used. In the American Midwest, however, fresh challenges emerged, as the cold caused the metal to contract, creating the risk of measurement errors. Soon, winter measurements were done only after a fire was used to warm the chain, expanding it back to its proper length.

You can see the squaring effect of Gunter’s Chain on the landscape anytime you fly over the United States, especially away from the older settlements of the East Coast.

Aerial view of Hancock County, Iowa. Photo credit: Dennis Dimick.

A settlement in the middle of nowhere, following a square layout based on surveys.

Cities are also laid out according to multiples of Gunter’s Chain. As the Utah Geospatial Research Center notes, Portland went with small square city blocks, of 198 feet—or 3 chain lengths. Salt Lake City went bigger, 660 feet by 660 feet, or 10 chain lengths. San Francisco and Phoenix decided to measure out rectangular blocks, which are 10 chains by 3 chains in San Francisco and 10 chains by 5 chains in Phoenix.

And for those of you who are cricket fans, you’ll be pleased to note that the cricket pitch is precisely one chain long, another enshrining of measurement in our lives.

However, the innovations from the French Revolution to Gunter’s Chain didn’t eliminate arbitrary measurement. In Britain, for example, there remained issues with arbitrary, old measures, captured even in more familiar Victorian history, as one contributor to Charles Dickens’s journal All the Year Round complained of hobbits:

If [I buy wheat] at Wrexham, [I must order] by the hobbet of one hundred and sixty eight [pounds]. But, even if I do happen to know what a hobbet of wheat means at Wrexham, that knowledge good for Flint is not good for Caernarvonshire. A hobbet of wheat at Pwlheli contains eighty-four pounds more than a hobbet at Wrexham; and a hobbet of oats is something altogether different; and a hobbet of barley is something altogether different again.

We’ve come a long way from these nasty little hobbitses of varying size and weight, but problems persist.

Hundreds of years after the Vasa tipped over, a similar mistake was made by NASA, in which the 1999 Mars Orbiter was lost, either smashed to bits or floating off into vast, empty space. It turned out the Jet Propulsion Laboratory made measurements in the metric system, whereas Lockheed Martin used inches and pounds. About half a billion dollars (in today’s value) was wiped out due to a conversion error. Our attempt to control the world through perfect measurement had, yet again, failed.

And now, a new problem has emerged. Like the medieval enthusiasts of the mensura Christi, we’ve made a cardinal error: conflating that which is measurable with that which is important and good.

The Tyranny of the Easily Measured

As the physicist Richard Feynman once quipped: “If our small minds, for some convenience, divide this…universe, into parts…remember that nature does not know it!” Humans are category creatures, with brains evolved to break down the information explosion that is our world—and cram it into neat and tidy little boxes that we can more easily understand. But nature doesn’t care how our brains make sense of reality.

In the last several decades, we have studied ourselves with ever-greater amounts of data, which has produced ever-greater quantities of social hubris, a misplaced certainty that we can understand and tame our world. And yet, over and over, we get walloped by the unforeseen and the unexpected, from populist demagogues and financial meltdowns to wildfires and wars. The diagnosis continues to be mistaken: that we just need better data. The mantra of arrogant tech bros has become a hidden assumption of modern life: to control the world, measure it. Spreadsheets will set us free.

I’m a staunch believer in the value of data, evidence, and measurement. But not all that is important can be measured. And, unfortunately, we too often fall into the trap of convenience bias: conflating that which can be easily measured with that which is most important. It’s a sin of metrology, because no system of measurement—no matter how standardized—can tell you whether it’s worth measuring something in the first place.

And yet, we remain stuck in what we might call the tyranny of the easily measured, in which the pursuit of standardized metrics has, at times, blinded us. For example, the solidity of economic measures like GDP doesn’t always mean that it’s the right way to conceptualize lived prosperity. We should interrogate systems of measurement more, for as we have seen, the objective veneer quickly crumbles and exposes its subjective, accidental features once the history of metrology is understood.

The lesson, though, isn’t to abandon centuries of innovations in accurate measurement. Instead, it’s to recognize that all measurement is a somewhat arbitrary subdivision of reality, an agreed-upon mirage of human creation, imposed on an interconnected whole. Metrology has come a long way since the ancient Egyptians, but we would be fools to think that we have somehow escaped from the slippery challenges that have always plagued the science of measurement, or to think that we always know what to measure.

And, most importantly, we should recognize that measurement doesn’t just categorize the world, it always creates something new, by making us think differently about the world and our place within it.

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