When the first skyscrapers appeared in cities across the world, they were greeted with an almost-unbroken chorus of praise for their pioneering spirit of innovation. In fact, the term “skyscraper” is so apt because it suggests that these new buildings were ‘scraping’ society’s technological horizons, a feat that required a number of significant engineering and design advances, including steel, safe elevators, electric arc welding, and fluorescent light bulbs (which allowed people to work safely and efficiently with less heat).

But what about those strange, protruding structures that crown some skyscrapers? Spires and antennas are two common rooftop elements, both of which serve important purposes.

Throughout the history of architecture, there has been a constant quest for height. This is the reason that spires are so common; they can add a significant amount of height to a building, and at relatively low cost.

Spires are also popular because they provide an opportunity to show off. In a time when so many buildings are cloaked in bland corporate exteriors, they can be adorned with fancy lights, flags, and other decorations to attract attention, generate revenue, or signal their status as the tallest building in their city.

One of the biggest complaints about modern skyscrapers is that they seem to be engaging in a sort of competitive arms race for height. The 408-foot mast on top of One World Trade Center, for example, was added to allow it to claim the title of the tallest building in the Western Hemisphere, and rise to 1,776 feet—a symbolic nod to American democracy’s birth date.