For my writing purposes, Gregory D. Bell’s Logistics of the First Crusade: Acquiring Supplies Amid Chaos (2020) was a must-read book. I want to sing my praises of Bell’s work.

His examination of how a large medieval army fed itself during a long march and several sieges is fascinating in its own right. But the diamonds in this book are the host of specific calculations. Bell makes some of the calculations himself, and he pulls others from good research by Donald W. Engels, John Haldon, and others. Together, though, all the calculations add a lot of clarity to why events on the ground unfolded as they did.

Where to start? Bell’s explanation of how the crusade’s military leaders had to secure numerous ports, towns, and castles simply to have the bases of supply necessary to sustain their army during the siege of Antioch is loaded with useful calculations for any medievalist fiction writer trying to achieve some level of realism.

The calculations cover three scenarios: army sizes of 30,000, 60,000, and 100,000. According to Bell’s calculations, a 100,000-soldier army would need around 183 tons of unmilled grain each day. Building upon the work of other scholars, he provides the amounts necessary for meeting the needs of individual soldiers (3 pounds of bread daily, or 3.66 pounds of unmilled grain), horses (4.85 to 13.2 to 26.4 pounds of fodder or pasturage daily, depending on the type), and oxen (15.4 to 24.2 to 48.4 pounds and ~eight gallons of water) (71, 104).

Looking at the weight totals alone, you can easily see why coastal and river marches were close to mandatory and why fleets typically crawled along the coasts when possible. If only 200 horses could fight by the end of the siege, as one source asserts (104), you can understand why after Bell points out that 1,000 horses would consume daily “roughly ten and a half tons of grain and hay” (104).

A standard Mediterranean galley might carry 30 to 36 deadweight tons, but normal crews, including defensive fighters and about 100 rowers, numbered around 150. Bell estimates that the crew members themselves weighed about 11 tons and that they would drink about four tons of water during a three-day crossing (107, 109). Add the weight of food, gear, and arms, and Bell estimates that one galley could carry about 10 tons of additional cargo (i.e., grains).

A large round ship might carry 200 to 246 deadweight tons, but such ships were far less common than the smaller ones. Mixed fleets of large and small ships could carry significant amounts of cargo, but demand at this scale was extremely difficult to fulfill for long periods.

Shortages of wagons, river boats, barges, and hauling animals complicated the task of moving supplies from centers to the field army, and the usual food scarcity during winters compounded the problem (114–116).

One last takeaway: in medieval times, a large, stationary army with lots of cavalry would struggle to avoid the onset of starvation itself during any long siege.