Reaching for the Sky

The tall towers that define the skyline of many modern cities are so familiar that it is easy to forget how recent they are. For most of history, the height of buildings was strictly limited, and even the grandest structures rarely rose more than a few storeys above the street. The appearance, little more than a century ago, of buildings soaring to ten, twenty or more floors marked a genuine revolution in construction. It was made possible not by a single invention but by the coming together of several developments, each of which removed one of the obstacles that had always kept buildings low.

The first obstacle was the weight of the building itself. In traditional construction, the walls carried the entire load of the structure, so that the higher one wished to build, the thicker and heavier the walls at the bottom had to be. Beyond a certain height this became impractical: the lower walls would need to be so massive that they would take up much of the ground space and leave little room inside. A building could not simply be piled ever higher, because it would eventually be crushed by its own weight. This limitation had constrained builders for thousands of years, and overcoming it required a completely different way of thinking about how a building stands up.

The solution was to change what held the building up. Instead of relying on thick outer walls to bear the load, engineers developed a strong internal skeleton, a framework of columns and beams that carried the weight of the whole structure. With this frame doing the work of support, the outer walls no longer had to hold anything up. They became a light covering, a skin hung on the frame merely to keep out the weather, rather than a massive structure bearing the building's weight. Freed from their old role, the walls could be thin and could even be made largely of glass, and the building could rise far higher than before without its base becoming impossibly bulky.

The material from which these frames were built was crucial. A frame strong enough to carry a tall building needed a material that was both strong and comparatively light, and that could be made in long, straight lengths. The development of cheap, reliable methods for producing large quantities of strong metal met exactly this need, giving builders beams and columns that could bear great loads without excessive weight. Later, the combination of this metal framework with another building material, poured around it to add strength and protect against fire, produced structures that were stronger still. These materials, more than anything else, made the tall building physically possible.

Yet even a building that could stand up would be useless if people could not reach its upper floors. Climbing many flights of stairs is exhausting, and few would wish to live or work near the top of a tall tower if they had to do so on foot. The tall building therefore depended on a second, equally important innovation: a safe and reliable means of carrying people quickly up and down. The invention of a lifting device that would not fall even if its rope broke was the key. Once people could be raised effortlessly to the highest floors, those floors became just as usable as the lower ones, and the full height of a building could be put to practical use.

These technical advances answered a growing need. In the crowded centres of rapidly expanding cities, land was scarce and expensive, and there was intense pressure to make the most of every available plot. Building upward allowed far more usable space to be created on a small area of ground than building outward ever could. Where land was most costly, the incentive to build tall was greatest, and the new towers rose fastest in exactly those places where space at ground level was in shortest supply. The tall building was thus as much an economic response as a technical achievement.

Since those early days, towers have climbed ever higher, and building them has raised fresh challenges, from resisting the force of strong winds to moving large numbers of people efficiently within a single structure. Modern towers rely on sophisticated engineering to remain stable and comfortable at great heights. Yet the basic principles that made them possible remain those worked out over a century ago: a strong internal frame to carry the weight, light materials to build it from, and a reliable way of moving people between the floors. Together these ideas lifted the roofs of cities into the sky, and they continue to shape the way people build and live in the crowded centres of the world.