What happened when the grain ships didn't reach ancient Rome?

In the year 51, Rome had food left for fifteen days. The richest city on earth didn't grow its own bread. It waited for ships. What happened when the grain ships didn't reach ancient Rome? The Roman grain supply, famine, bread riots, and the emperors who lived in fear of a late fleet. Rome's bread came from North Africa and Egypt, across the Mediterranean, in some of the biggest ships of the ancient world. From November to March the sea was closed. A poor harvest, a late fleet or a few ships lost, and by the end of winter the city was counting sacks. We follow one sack of grain from a field beside the Nile to a room five floors up in Rome, then watch what happened every time the chain broke. Pompey sailing into a storm because "to sail is necessary, to live is not". A crowd trapping the Senate and begging Augustus to take the grain. An emperor pelted with bread in the Forum. A city under siege grinding its last grain on mills floating in the Tiber. CHAPTERS 0:00 Fifteen days of food left 0:59 Fifteen days 2:05 Where your bread came from 3:20 The ship 4:24 The sea closes 6:06 The fleet comes in 6:46 The last miles 8:02 The bread line 9:44 Grain is not bread 11:07 57 BC: "We have to sail" 12:06 22 BC: make him dictator 13:19 AD 6: fewer mouths 14:36 The waves 15:10 Seven days 16:11 The emperor and the bread 17:27 The emperor's deal 18:29 Every time the ships were late 19:55 Bread and circuses 20:56 The mills on the river 21:46 When the ships stopped for good SOURCES • Tacitus, Annals 3.54, 12.43; Histories 4.52 (the fifteen days; Claudius in the Forum; the ten days of AD 70) • Suetonius, Julius 41; Augustus 40-42; Claudius 18-20 (the grain list; the crust-throwing crowd; Claudius's rewards for shipbuilders) • Cassius Dio 38.13, 54.1, 55.26, 59.17, 60.11, 73.13 (free grain; the crowd and the rods of office; the AD 6 expulsions; Caligula's bridge of boats; the harbour at Ostia; Cleander) • Res Gestae Divi Augusti 5, 15 • Josephus, Jewish War 2.383-386 (North Africa eight months, Egypt four) • Lucian, The Ship 5-9 (the grain ship Isis at Piraeus) • Vegetius, Epitome of Military Science 4.39 (the sailing season) • Seneca, Letters 77 (the Alexandrian mail boats at Puteoli); On the Shortness of Life 18 (seven or eight days) • Pliny the Elder, Natural History 18.107 (no professional bakers before the war with Perseus) • Livy, Periochae 60; Plutarch, Gaius Gracchus 5 and Pompey 49-50 (Gracchus's grain law; "to sail is necessary") • Cicero, Letters to Atticus 4.1; Pro Sestio 55 • Juvenal, Satire 10 (bread and circuses) • Ammianus Marcellinus 19.10 (Tertullus, 359) • Procopius, Wars 5.19 (the floating mills of 537) • Claudian, The War Against Gildo (Rome's speech); Hydatius, Chronicle (Carthage, 439) • Glenn Storey, "The population of ancient Rome," Antiquity 71 (1997); estimates collected in Twine (1992); Platner and Ashby (1929) on the Horrea Galbana WHERE THIS IS LESS CERTAIN Rome's population is an estimate. "Perhaps a million" is the conventional figure; some historians argue for about half that. The fall to around thirty thousand by the sixth century comes from modern estimates, and the grain supply was only one cause among sieges, sacks, plague and war. The dimensions of the Isis come from a single writer, Lucian. Dio's claim that the grain official made the shortage of 190 worse on purpose is his account of a court intrigue; Herodian tells it differently and blames Cleander himself for buying up the grain.