Karl Marx and Friedrich Engels first met in Cologne, in November 1842, at the office of the Rheinische Zeitung where Marx was active as its young editor. But their theoretical partnership began only in 1844, in Paris. Engels, the son of a textile industrialist, had already had the opportunity to travel in England, seeing for himself the effects of capitalist exploitation on the working classes.

An article of his on the critique of political economy, published in the Franco-German Yearbooks, aroused great interest in Marx, who at the time had decided to devote all his energies to the same subject. The two then began a theoretical and political collaboration that would last for the rest of their lives.

In 1845, when the French government expelled Marx because of his Communist activities, Engels followed him to Brussels. That same year saw the publication of one of their few jointly written works ~ The Holy Family, a critique of the idealism of the Young Hegelians.

The two also produced a voluminous unpublished manuscript ~ The German Ideology ~ that was left to the “gnawing criticism of mice”. Subsequently, with the first signs of the 1848 revolutions, Marx and Engels brought out what would become the most widely read political text in the history of humanity ~ the Manifesto of the Communist Party.

In 1849, following the defeat of the revolution, Marx was forced to move to England, and Engels soon crossed the channel after him. Marx stayed in London, while his friend went to manage the family business in Manchester, some three hundred kilometres away. From 1850 to 1870, when Engels retired from business and was finally able to rejoin his friend in the English capital, the two men lived the most intense period of their lives, comparing notes several times a week on the main political and economic events of the age.

Most of the 2,500 letters they exchanged date from these two decades, during which time they also sent some 1,500 items of correspondence to activists and intellectuals in nearly twenty countries. To this imposing total should be added the 10,000 letters to Marx and Engels from third parties, and another 6,000 which, though no longer traceable, are known with certainty to have existed. It is a priceless treasure, containing ideas which, in some cases, they did not succeed in fully developing in their writings.

Few nineteenth-century correspondences can boast references as erudite as those that flowed from the pens of the two Communist revolutionaries. Marx read eight languages and Engels mastered as many as twelve; their letters are striking for their constant switching between different languages and for their number of learned quotations, including the use of ancient Latin and Greek.

The two humanists were also great lovers of literature. Marx knew passages from Shakespeare by heart and never tired of leafing through his volumes of Aeschylus, Dante and Balzac. Engels was for a long time president of the Schiller Institute in Manchester and worshipped Aristotle, Goethe and Lessing.

Along with constant discussion of international events and revolutionary possibilities, many of their exchanges concerned the major contemporary advances in technology, geology, chemistry, physics, mathematics and anthropology. Marx always considered Engels an indispensable interlocutor, consulting his critical voice whenever he had to take a position on a controversial matter.

At times their relationship involved a veritable division of labour. Of the 487 articles published in Marx’s name between 1851 and 1862 in the New York Tribune (the paper with the largest circulation in the United States), nearly a half were actually written by Engels. Marx wrote for the American public about economic crises and major events in world politics, while Engels recounted the course and possible outcomes of the many wars that took place. In this way, he enabled his friend to devote more time to the completion of his economic studies.

The relationship between the two men was even more extraordinary in human terms than at an intellectual level. Marx confided all his personal difficulties to Engels, beginning with his terrible material hardship and the numerous health problems that tormented him for decades. Engels showed total self-abnegation in helping Marx and his family, always doing everything in his power to ensure them a dignified existence and to facilitate the completion of Capital. Marx was ever grateful for this financial assistance, as we can see from what he wrote one night in August 1867, a few minutes after he had finished correcting the proofs of Volume One: “I owe it to you alone that this was possible.”

From September 1864, Marx’s involvement in the activity of the International Working Men’s Association caused further delays to his magnum opus. From the outset he had assumed the major burden of its leadership, but Engels, too, as soon as he could, placed his political talents at the service of the workers.

On the night of 18 March 1871, when they received news that the “storming of the heavens” had succeeded and that the first Socialist commune in human history had come into being in Paris, they understood that the times could change faster than they themselves had expected.

Even after the death of Marx’s wife in 1881, when the doctors prescribed trips far from London in an attempt to cure his ailments, the two men never stopped writing to each other. Often they used the affectionate nicknames by which various comrades in the struggle addressed them: the Moor and the General ~ Marx because of his jet-black beard and hair, Engels because of his extensive knowledge of military strategy.

Shortly before his death, Marx asked his daughter Eleanor to remind Engels to “make something” of his unfinished manuscripts. Engels respected Marx’s wishes and began that gigantic task soon after the afternoon in March 1883 when he saw him for the last time. He would survive Marx by twelve years, much of which was taken up with preparing for publication of the draft material for Volumes Two and Three of Capital that his friend had not managed to complete.

During that last period of his life, Engels missed a lot of things to do with Marx, including their constant exchange of letters. As he carefully catalogued their correspondence, he remembered the years when, drawing on his pipe, he had been in the habit of writing a letter late at night.

Now he often re-read them with a touch of melancholy, thinking of all the moments in their youth when, smiling and joking to each other, they had tried to predict where the next revolution would break out. Never, though, did he abandon the certainty that many others would continue their theoretical labours, and that millions, in every corner of the world, would press on with the struggle for the emancipation of the subaltern classes.

The writer is Associate Professor of Sociological Theory at York University, Toronto, Canada. He has authored and edited several books on Marx