It is easy to forget that the reliable, cheap delivery of letters is a relatively recent invention. For most of recorded history, communication at a distance was the privilege of governments, wealthy merchants and religious institutions. Ordinary people who wanted to send a message over any significant distance had to entrust it to travellers, pay a courier, or wait for chance. The transformation of this situation, and its extension to the general population, took place in the nineteenth century, driven by administrative reformers whose influence is now often underestimated.

The British postal reform of 1840 is usually treated as the starting point. Before that year, the cost of sending a letter in Britain was calculated according to the distance travelled and the number of sheets, and was paid by the recipient. A letter from London to Edinburgh could cost a working family the better part of a day's wages, and it was routine for recipients to refuse delivery. The reformer Rowland Hill proposed two innovations: a flat rate of one penny for letters up to half an ounce, regardless of distance, and prepayment indicated by an adhesive stamp. Both were adopted, and the volume of letters in Britain more than doubled within a year.

Hill's scheme depended on several less visible changes. Sorting became mechanised to a modest degree, with gauges that separated letters by thickness and standardised racks that speeded hand-sorting. The railway network, then expanding rapidly, allowed letters to move much faster than by road. The treasury, initially sceptical that a flat rate would cover costs, was eventually persuaded by the argument that a larger volume of letters, more efficiently handled, would produce revenue despite the lower price per item.

Other countries followed within a few decades. France adopted a flat rate in 1849, Germany (through the Thurn und Taxis system and later the imperial post) in 1850, and the United States in 1863. International post was unified through the General Postal Union, founded in 1874 and later renamed the Universal Postal Union, which set common rates and procedures for cross-border mail. Historian Dr. Elena Marchetti has argued that the Universal Postal Union is one of the earliest effective international organisations, predating most diplomatic bodies and surviving through world wars because its work was too useful to suspend.

The social consequences of cheap post were considerable. Literacy rates, already rising in most of western Europe, received a further push because letter-writing became a practical daily skill. Businesses that had depended on local markets discovered that they could reach customers across countries, and mail-order catalogues, which flourished from the 1870s, created national consumer markets well before railways alone would have produced them. Emigration, always dependent on information from those who had gone before, became more manageable when letters home arrived cheaply and reliably.

Cheap post also had political effects. Petition campaigns, subscription lists for new publications, and the distribution of pamphlets all depended on the ability to send small amounts of paper cheaply over long distances. Dr. Marchetti has linked the rapid growth of nineteenth-century reform movements - anti-slavery campaigns, women's suffrage societies, trade unions - to the availability of cheap post. The same tool, however, served governments as well as reformers. Census forms, tax notices and military call-up papers all travelled on the same network.

The modern era has both preserved and reshaped this infrastructure. Letter volumes in most high-income countries have declined steadily since the early 2000s as email and messaging applications have taken over personal correspondence. Parcels, on the other hand, have grown enormously, driven by online shopping. Postal services have responded by investing in delivery networks, sorting hubs and tracking systems, and most have shifted their business model from letters to parcels. Rural delivery, the operation for which the nineteenth-century reformers fought hardest, is in places now the most financially demanding service of all, and several countries have reduced its frequency in recent years.

Rowland Hill would recognise much of the result. A flat rate still applies to letters in most countries, prepaid stamps remain in use, and recipients no longer refuse delivery. The mail is no longer the newest communication technology, but it has quietly become one of the most durable, precisely because it was designed from the start to be as simple as possible.