Zhuge Liang's army moved supplies on single-wheel barrows

During Zhuge Liang's northern military campaigns against Wei (231–234 CE), supply lines through the narrow, steep mountain passes of the Qinling range could not accommodate the standard two-wheeled ox carts used on flatter terrain, forcing reliance on human porters who could each carry only as much grain as their own body could bear over the distance — a hard ceiling on supply-line throughput no matter how many additional porters were assigned.

The Sanguozhi (Records of the Three Kingdoms), the primary historical source for this period, credits Zhuge Liang with fielding an improved single-wheeled barrow — the 'wooden ox' and 'flowing horse' — for these campaigns, carrying a reported capacity on the order of a year's grain supply, roughly 200 kilograms or more, per unit.

Centered the load on one wheel, shifting weight from muscle to a pivot, so a porter steered instead of carried, tripling what one person could move.

A wheel bears weight through rolling contact, not muscle, so the porter's physical limits no longer cap load size.

One wheel needs far less clearance than a cart, so it fits terrain too narrow for animal-drawn vehicles.

The porter's role changed from bearing weight to steering, a task with much higher endurance, raising per-person throughput.

Adding porters only repeats the same per-person ceiling, while the wheel raises the ceiling for every operator.

When a process is capped by what one person can bear, shift the load onto a mechanical intermediary so the operator steers instead of carries.

The Sanguozhi credits these vehicles with sustaining Zhuge Liang's supply lines through mountain terrain that had previously constrained his campaigns' logistical reach, and the underlying single-wheel-load principle is recognized in the history of engineering as a documented early form of the wheelbarrow, appearing in Chinese sources roughly a millennium before comparable wheelbarrow use is documented in Europe.