The Serengeti is fifteen thousand square kilometres of grass in northern Tanzania, flat to the horizon, and the two million wildebeest, zebra and gazelle on it are walking a circle that never stops. Most people know one minute of it: the Mara River crossing in the far north, where the herds pile onto the bank, hesitate, then pour through while crocodiles work from below. That is July into October, one station out of twelve. The ring runs 800 to 1,000 kilometres, driven by rain and new grass rather than any calendar. In January and February the herds are far south around Ndutu, dropping their calves within a few weeks of one another, thousands a day at the peak. A newborn is up on its legs within minutes, and it needs to be: lion, cheetah and hyena work the edges. By June they are west at the Grumeti; by December the short rains have brought them back to where they started. The grass is short and rich because the ground is not soil but ash from the Ngorongoro highlands. Without it the circle would not turn.
Out on the plain the only things standing above the grass are the kopjes, outcrops of granite among the oldest rock in Africa, each a patch of shade and a lookout that lions and cheetahs climb. A dawn drive works that ground. You are out at first light, while the lions are still in from the night and the cheetahs use the cool hour to travel. They ignore vehicles here, so your driver can stop beside a resting pride and leave you there while the cubs tumble under their mother. The same hour brings out what the migration overshadows: elephant families in file, calves walled inside. Balloons lift from Seronera in the half-light every day of the year, low enough to show you the herds as lines rather than dots. The circle brings them back past the same rocks within a few weeks of last year. The lion asleep on one of those rocks is among the few things out here that never has to move.