The most obvious ingredient in cake, one of the few that must be present for a thing to be a cake, is flour. You can make cakes without eggs, without sugar or honey, and with different different types of leavening, but the flour is the binder and the base of a cake.
A flour is a powder ground from a plant; the major baking flours across the world are cereal grains. The five most common types of culinary flours are also among the oldest:
- Wheat: Used worldwide, and is the most common baking flour in North America and Western Europe. Wheat contains gluten, a protein that helps bread (and cake) dough bind together, trapping the expanding gas created by yeast and other leavening agents, so the dough rises.
- Rice: Ground from rice kernels, this gluten-free rice has been popular in Asia for thousands of years, and is growing popular around the world as an ingredient in gluten-free foods. (“Glutenous” rice is stickier, but doesn’t actually contain gluten.)
- Rye: A low gluten (but not gluten-free) flour common in breads, particularly in Eastern Europe, and in places where wheat doesn’t grow well because the soil is too sandy or peaty. Rye is also hardier than most wheats, able to survive even under a layer of snow. It’s not used for cake as often as wheat because of its strong flavor.
- Barley: As a flour for baking, barley has been used around the world; it was cultivated around the same time as wheat in the Middle East, and in China and India a short time later. However, barley is most useful to baking as a malt–it’s been an ingredient of beer since ancient times, and its yeast is used as a leavening for breads and cakes.
- Corn: Cultivated for at least 10,000 years, maize is a popular staple food in Mesoamerica, and gluten-free corn flour is one of its earliest uses. After the colonization of these lands by Spanish invaders, corn was introduced to Europe as well–though Spaniards worried it wasn’t nutritious because it wasn’t native to Europe, and wouldn’t use it as a substitute flour for communion wafers even after forcing the indigenous populations to convert to Catholicism, because Catholic doctrine stated only wheat could be transubstantiated into the body of Christ.  Corn flour is rarely used for cakes, though there are some interesting exceptions.
Flour developed almost immediately after the beginning of agriculture, but how it was processed has evolved over the millennia . Early bakers ground the grains by hand between stones, and this is true all over the world, for thousands of years. Romans experimented with water-driven mills, and they were popular for a while, but mechanical flour mills became mainstream in Europe in the middle ages with the introduction of the windmill, which probably originated in Persia a few centuries before.
By then, in Europe at least, the home cook could get wheat flour pre-ground, though the quality depended on the mill, the harvest, even the weather. Having access to mill-ground wheat didn’t necessarily mean that the average family had better food. They just had it without the extra work of grinding it themselves, and that savings in time made a huge difference in the (mostly female) cooks’ lives.
London’s first steam mill was erected in 1786, which moved flour production into the industrial age, which now produce hundreds of types of flour, billions of pounds a year. Now, getting flour is as easy as picking it up from the store, or ordering it off the internet. Now, we have a choice in what type of flour we want to use in our baking, and there are recipes to go with every choice. But think back to those earliest bakers, who had to bring wheat or corn or rice in from the field… who had to dry it, and grind it–by hand, pushing the kernels into a powder with a rock–for hours, just to get enough flour to make a loaf of bread.
When a serving of bread is the product of hours of work, how much more special then is cake?
 Rebecca Earle, The Body of the Conquistador: Food, Race, and the Colonial Experience in Spanish America, 1492-1700. New York: Cambridge University Press 2012, pp. 17, 151.