in the history of the world. In fact there were allegations, true or false, that every single one of the first dynasty of Roman emperors was murdered – from the poisoned figs (supposedly prepared by Livia) that were said to have finished off Augustus to Nero’s forced suicide after a military coup deposed him.

Winterling is right to point to the impact of these bloody transitions of power on the written history of the empire. Most senators during most reigns were collaborators (as most people are under most systems of power, however brutal); and when regimes changed they made every effort to reposition themselves, usually by excoriating in speech and writing, in ever more gory detail, the emperor who had been their friend. That writing is the Roman imperialDuring summer 2017 a large swath of Australia’s Great Barrier Reef—normally a riot of electric oranges, reds and other colors—turned ghostly pale.

Unusually warm water temperatures, partly due to global warming, had caused the corals to expel from their tissues the symbiotic algae that provide them with food and give them their brilliant hues. It was the second mass-bleaching event to hit the reef in as many years. Together, the back-to-back events hit two thirds of the reef.

Now, with the 2019 Australian summer poised to begin, atmospheric scientists are predicting an El Niño—a recurring period marked by warmer temperatures in the tropical Pacific Ocean. This potential for high temperatures again poses a threat to the Great Barrier Reef, one that marine biologist Terry Hughes—a high-profile champion of coral reef