Last month the world got to see the first image ever taken of a black hole. This groundbreaking moment in astronomy was made possible by international collaboration on a huge scale: eight linked telescopes in locations ranging from Chile to Spain to the South Pole produced the data to create the images. The project involved scientific institutions from every continent — a truly global effort.

International projects on this kind of scale are a relatively recent phenomenon, but cross-cultural collaboration has been a central feature of scientific practice for millennia. Ever since the beginnings of scientific research in the ancient world, scholars have traveled to learn, to share their ideas and to work with other like-minded people. Much of our scientific understanding of the world today emerged from these collaborations. And yet today, such cross-cultural work is under threat, as anti-immigrant, nationalist policies threaten a loss of intellectual resources that could lead to a significant reduction in scientific advances.

In the Classical period, Alexandria was the city scholars gravitated toward. Situated on the northern coast of Egypt, it was the center of the ancient Mediterranean intellectual world and home of the famous library. King Ptolemy I took over the city in 305 B.C. on the death of its founder, Alexander the Great. He immediately began transforming it into a vibrant seat of learning, amassing scrolls for his collections, tempting the brightest minds to make the city their home.

The knowledge stored in the library was also the product of many civilizations: Babylonian, Egyptian, Jewish, Persian, Hellenistic and later on, Roman. This made it an incredibly valuable, pan-cultural resource, enabling some of the most important scientific books of all time to be written there, using data from much older traditions. The library helped Alexandria to retain its reputation as an unparalleled center of learning for several centuries. Six hundred years after Ptolemy I died, clever young men were still boarding ships bound for the great city so that they could study everything from Homer to human skeletons.