The tea-horse road
Overland routes between the tea-growing areas of Yunnan and Sichuan and the Tibetan plateau exchanged tea for horses over a long period. The journey took months across difficult terrain, which is why the tea sent along it was compressed into bricks and cakes. Compression was a transport solution first; its role in ageing was a consequence discovered later, and it is now the reason the format survives.
Maritime routes to Europe
Sea routes from Chinese ports to Europe carried tea in quantity from the seventeenth century, and speed mattered commercially — the clipper races of the nineteenth century were about getting the new season’s tea to market first. Long sea voyages also favoured fully oxidised tea, which is stable in a way green tea is not, and this is part of why Europe became a black-tea market while China remained a green-tea one.
The overland route to Russia
Caravan routes across Siberia carried tea to Russia over journeys of many months. The Russian Caravan blend’s smoky character is popularly attributed to campfires along the route; that story is folklore, and the smokiness in a modern blend comes from deliberately including a smoked tea. The route itself is documented; the flavour explanation is not.
How transport shaped the product
Read across the routes and a pattern appears. Compressed dark tea for overland journeys where weight and durability mattered. Fully oxidised black tea for sea routes where stability mattered. Delicate green tea staying largely where it was made. The map of what the world drinks still substantially reflects the logistics of the period when the trade was established.