Stairs are just an extension of the floor, which in turn is really just an extension of the earth. What makes the floor unique is that it’s separated from the earth for obvious reasons. Buildings literally start to rot the second they’re exposed to the earth and its elements. Floors are lifted off the ground to keep occupants warm and dry. This simple gesture preserves the structural system and floor materials. Wood of all sorts has always been an efficient choice for both. Especially for walking surfaces. Wood is soft and rugged. Historically hand laid stone, brick then tile likely came next.
One of the most durable architectural materials is masonry and one of the most enduring configurations the arch. The arch had been around for a while but the Romans made it famous and took the form to a new level. There are a wide variety of different arch shapes, created and adapted over time in various ways. The barrel vault, groin vault and rose window are also kinds of arches. Bust the most impressive arch could be said to be the dome. One particularly striking example is the dome at Hagia Sophia in Turkey built in the 6th century. Not only is this dome massive, but it utilizes a structural form called the pendentive.
But sometimes the most profound ideas are simple. The covered porch entrance or walkway, also called the portico, was an important innovation not only for the Egyptians, Greeks, Romans but for humankind. It is a building form that not only caught on but has been repeated and developed extensively, particularly in monumental architecture. A portico gives a building character. It also provides a sense of arrival and protection from the elements. The emperor Hadrian rebuilt the Pantheon in Rome, Italy in 126 AD; it had a portico. Hundreds of years later Andrea Palladio used the portico broadly. Neoclassical architecture like Thomas Jefferson’s Monticello depends on the form as a reference to the past. And we still see remnants of the portico, distilled down to simple roof forms and piers, in modern architecture and the contemporary work of today.