Everyone remembers the cavalry charges and the siege towers. Far fewer know about the other army that marched behind Ale...

Everyone remembers the cavalry charges and the siege towers. Far fewer know about the other army that marched behind Alexander the Great, one made up of doctors, engineers, historians, philosophers, surveyors, translators, and even actors. When Alexander crossed the Hellespont in 334 BC, 2,360 years ago, his forces had no detailed map of Asia. A group of specialists called bematists, trained distance measurers who counted their own steps across thousands of miles, turned the unknown terrain into a sequence of calculable routes. Two of them, Diognetus and Baeton, are named in the ancient sources. Without their work, moving and supplying tens of thousands of soldiers and animals would have been a logistical nightmare. The engineers were equally critical. Diades and Charias, students of the military engineer Polyidus of Thessaly, designed siege towers, battering rams, and drilling machines built to be disassembled, transported, and reassembled at the next city's walls. The seven-month siege of the island city of Tyre in 332 BC, which required building a causeway from the mainland and converting ships into floating ram platforms, was one of the most complex engineering operations in the ancient world. Callisthenes of Olynthus, a relative and student of Aristotle, traveled as the campaign's official historian, framing the conquest in heroic, pan-Hellenic terms. His relationship with Alexander collapsed when he refused to perform the Persian ritual of proskynesis, a deep bow reserved in Greek tradition for the gods. In 327 BC he was arrested on suspicion of involvement in an assassination plot. Ancient sources disagree on whether he was executed or died in prison. Philosopher Anaxarchus of Abdera also accompanied the campaign, most notably consoling Alexander after the king drunkenly killed his own general Cleitus the Black at a banquet in Samarkand in 328 BC. In India, Alexander's doctors met treatments they had never encountered. When Greek medicine had no answer for certain venomous bites, local healers were brought in. The physician Philip of Acarnania, Alexander's personal doctor since boyhood, had already saved the king's life in Tarsus in 333 BC when a s...