The comedian Eddie Izzard has a bit in her show Dress to Kill where she characterizes colonialism as sticking a flag in the ground to claim a place, then ignoring the assertion of the locals that their home is their own because, well, they don’t have a flag, do they?

While obviously exaggerated for the purpose of comedy, the idea in play there isn’t without basis in fact. Nowadays, flags are the premier emblem of a country — and often smaller units thereof as well, like provinces and states and even cities. We march our flags in the parade of nations that starts off the Olympic Games; we brand our exports with them. We fly them high over our governmental buildings and lower them to half-mast in the wake of tragedy, as a signal that the whole community is (or should be) in mourning.

Flags probably have their origins in a military context, and we’ll get into how they were used there more in the next essay. Fabric banners, as opposed to standards more broadly, may have been invented twice: one in south or eastern Asia, the other in ancient Rome, though I can’t swear that there wasn’t influence from former on the latter. They can be attached to the side of a pole, to a horizontal cross-bar at the top, or both; the advantage of a horizontal attachment is that you’re not dependent on wind to lift the flag and display its design.

Nowadays almost all flags are not only rectangular but adhere to one of a small number of ratios in their proportions (2:3, 1:2, or 3:5). There are still exceptions, though, and they used to be more common. If you look at the state flag of Ohio, you’ll see an example of a swallowtail pennon: a flag wider at the hoist (attachment) than at the fly (loose edge), with a forked edge rather than tapering to a triangle point. Heraldic rules used to dictate who carried what style of flag at what size, along with what could be placed on the flag; for example, differentiating a banner from a pennon helped differentiate a knight banneret from a knight bachelor.

Speaking of heraldry . . . As you might expect, a lot of early European flags consisted of sticking one’s heraldic arms on a pole. Because of that, the rules governing design ensured a fairly high degree of clarity, like you would want on a battlefield. But the intersection of various emblem traditions has in modern times produced some fairly terrible flags, especially at the level of cities: the city has a seal, and it needs a flag, so it just sticks the seal on a flag and calls it a day. The result is a fiddly, complex image nobody would ever have bothered with if they needed to embroider or appliqué the entire thing, instead of mechanically printing it.

The term for flag design is vexillography, and boy howdy do people in that field have Opinions about the right way to go about it. These days, there’s general agreement that a flag should be relatively simple — often characterized as “a child could draw it.” Many countries have adopted a triband, i.e. a flag divided into three bands either horizontally or vertically, which may or may not be equal in width. Some of these have a “charge,” an emblem of some kind superimposed, usually at the center (but not always). When each band is a different color, it’s termed a tricolor, and since the late sixteenth century, that style has been associated with republicanism and revolution. As democratic governance has spread around the world, tricolors have followed — though of course nothing stops a government from adopting that design as a fig leaf over very un-democratic rule!

Of course, these get very repetitive, and (outside their charges) they can fill up the available color design space very fast. Modern flags often depart from the heraldic rules for tinctures, both in the colors they use and how they’re positioned. The green/yellow/red of Pan-Africanism or the black/white/green/red of Pan-Arab nationalism don’t always avoid putting a color against a color; the flag of Argentina specifies a pale blue instead of the more midline hue seen in many other flags. Non-triband flags also sometimes reach for ways to distinguish themselves from the herd; the redesign of Minnesota’s state flag (which used to be a poster child for bad design) cleverly inverted the sideways triangular charge called a “pile” so as to echo the shape of the state itself. When everybody has a flag, it helps to get creative!

But the reason we need so many flags boils down to modern nationalism. It’s not that kingdoms didn’t have banners in the past — they absolutely did, on the battlefield and in their castles — but often those banners were simply the arms or emblem of the ruling dynasty. Or a country might use multiple flags in different contexts, like sixteenth-century Spain flying both the arms of the Habsburg king and the saw-toothed Cross of Burgundy (that one deployed particularly on ships). As national identities coalesced in the late eighteenth century, though, it became increasingly important to have a national symbol separate from the person in charge, and those symbols appeared more and more often in contexts other than military ones.

Not that flags have ever been limited to military use. Taken in the general sense of “a piece of fabric meant to fly in the wind” rather than the distinctive emblem of a person, group, or locale, flags can serve all manner of purposes! Signal flags came up in Year Eight as a means of communication; Tibetan prayer flags are flown to spread their blessings on the wind. We use flags to mark everything from the finish line of a race to where your tour guide is in the crowd (though when you get down to it, that latter is probably a direct descendant of their role on the battlefield . . .). When a player commits an offense in certain sports, we signal it with a flag. When a city wants to advertise a festival or a special museum exhibit, they may dangle banners from the streetlights.

And when they want to assert their right not to be governed by a colonial power, they might just design a flag.