Retaining Walls With Character, Moxie, Whimsy, Artistry...

By Leslie McGuire, managing editor

Even though the top of this wall has to be straight, that is mitigated by the bottom line which pulls the eye up to an imaginary point in the distant perspective. This, along with the designs in the block, gives an enhanced sense of endless view. In addition, the curving planting beds at the base soften the angularity.
Photo courtesy of Keystone

Starting with the premise that Form Follows Function, consider the possibilities and vistas that could open up if Form followed Function while Following the Contours of the Land…or the thoughts inherent in rocks…or the ebb and flow of the shoreline…or the dreams of hills—even if they existed a million years ago.

“Work with me here,” says Mother Nature when faced with a retaining wall project. But does anyone listen? Nature as we all know, if not properly contained, will regain her natural curves—sometimes with a vengeance. But why not try to work with those curves?

Above & Below: The Great Wall is one of the largest building construction projects ever completed. It stretches across the snakelike mountains of northern China, winding north and northwest of Beijing. It is constructed of masonry, rocks and packed-earth and is over 3,100 miles long. The Great Wall can be seen from Earth orbit, but, contrary to legend, is not visible from the moon, according to astronauts Neil Armstrong, Jim Lovell, and Jim Irwin.

After all, why does a retaining wall have to be a block driven, rectangular, fascistic collection of squares that disrupt the eye, eviscerate the view while imposing it’s mechanistic shape onto an otherwise sinuous landscape. Does design have to be driven by the shapes conceived of by quarry machines? Does form have to be trapped within the confines of medieval or feudal concerns? Michelangelo wasn’t controlled by the shape of his blocks of marble. His job, as he saw it, was to release the figures imprisoned in those blocks.

Retaining walls in ancient times were far more involved with maintaining the safety of the inhabitants from the invading hoards. They kept the people in and the mudslides of humanity out. Nowadays, retaining walls are designed to keep people safe from invasions of mere mud. The only difference is, they keep the ravening mudslides in and maintain the safety of the people who are out in the open space. Since there is no longer such a great need for walkways and gun turrets and crenallated towers to protect the archers, perhaps we can get a bit more creative with the forms.

Any city or state worth its salt had a really big retaining wall. The practice of strengthening civilian population centers to ward off attack began in the earliest years of human civilization. Ancient agricultural settlements were frequently prey to marauding bands of warrior-tribesmen. As early as 7000 BC the city of Jericho in Palestine, made famous through its destruction as told in the Old Testament book of Joshua, had a wall for just that purpose.

Recently, Greek archaeologists have unearthed the fortifications of a 2,350-year-old city on Crete marked by extensive signs of siege. The archaeologists discovered the remains of a fortified tower, a city gate and a 3.5-kilometer (2.2-mile) wall surrounding the ancient city of Aptera, near the port of Hania and dating to 4 BC, the ministry said.

Biblical Jericho’s Wall

The mound, or ‘tell’ of Jericho was surrounded by a great earthen rampart, or embankment, with a stone retaining wall at its base. The retaining wall was some 12 to 15 feet high. On top of that was a mudbrick wall six feet thick and about 20 to 26 feet high. At the crest of the embankment was a similar mudbrick wall whose base was roughly 46 feet above the ground level outside the retaining wall. Jericho is believed to be one of the oldest continuously-inhabited cities in the world, and archaeologists have unearthed the remains of over 20 successive settlements there, dating back to 9000 BC. The retaining wall did its job very well until its destruction in approximately 1550 BC. Rumor has it that was because of an earthquake, not necessarily a great horn player.

Some of the earliest examples of bas-relief appeared in the Babylonian, Assyrian and Hittite cultures. Bas-relief was also plentiful in ancient Egypt and Mesopotamia, and in China and India. Of course, examples of exquisite and detailed bas-reliefs from later periods when the Greeks and Romans made use of the technique can be seem in museums worldwide. This bas-relief wall is an example of modern techniques for retaining wall decoration.
Photo courtesy of Scott Systems inc.

Ninevah’s Gate Guarded Wall

Some cities got their local gods to help out with protection. Ninevah was a truly magnificent walled city. In c. 700 BC. Sennacherib laid out new streets and squares and built within it the famous “palace without a rival”, the plan of which has been mostly recovered and has overall dimensions of about 630 by 600 feet. At this time, the total area of Nineveh comprised about 1,800 acres and 15 great gates penetrated its walls. The enclosed area had more than 100,000 inhabitants. The wall protected those inhabitants for a time. But so did their bull deities.

At the entrance of cities, they were sculpted in colossal size, and placed as a pair, one at each side of the gates. Each bull god looked towards one of the cardinal points. However, this retaining wall needed more help than the gods apparently.

Providing plant-receiving cavities in the forward portions of modular wall blocks can be for aesthetic purposes and/or to minimize erosion of the soil fill material. One example of a plantable wall block is where the design of the block enables limited selectivity in set-back with the principal plant-receiving cavities being provided by the laterally staggered nature of the blocks in superimposed courses.
Photo courtesy of Leslie McGuire

The Great Wall of China

The Chinese had a transitional solution. They built a really, really big wall. In the words of Sun Tzu in The Art of War, and the Taoist classical literature of the Tao-te Ching, there is a better way.

“That is why high walls and deep moats do not guarantee security, while strong armor and effective weapons do not guarantee strength. If opponents want to hold firm, attack where they are unprepared; if opponents want to establish a battlefront, appear where they do not expect you”.

Using a combination of facing patterns, fountains, individual curved planting beds each holding a different kind of palm, plus a winding stream runnel, this elegant retaining wall not only controls a hillside, it also puts one in mind of a path along a stream on a trip back through history.
Photo courtesy of Leslie McGuire

Sun Tzu’s book was evidently written during the Warring States Period, so, after subjugating and uniting China, the emperor, among other things, connected and extended four old fortification walls along the north of China that originated about 700 B.C. (over 2500 years ago).

The Ming dynasty began in 1368, and lasted until 1644 A.D. Its founder was a peasant, the third of only three peasants ever to become an emperor in China. One of the great accomplishments of the Ming was the building of the Great Wall.

The Great Wall is one of the largest building construction projects ever completed. It stretches across the sinuous mountains of northern China, winding north and northwest of Beijing. It is constructed of masonry, rocks and packed-earth. It is over 3,100 miles long. Its thickness ranged from about 15 to 30 feet and was up to 25 feet tall.

In Roman wall design, Opus testaceum (C) referred to a concrete wall in which wedge-shaped pieces of brick were inserted, point first, so that the wall appeared to be of laid brick. Opus incertum (A) referred to a concrete wall in which irregular chunks of stone were pressed into the soft concrete. When the concrete set, the stones were chiseled down even with the concrete surface. Opus reticulatum, (B) or “netlike work” in which little square pyramids of stone were inserted point first in a diamond pattern, became quite popular.

The Fortified Walls of Ancient Crete

Recently, Greek archaeologists have unearthed the fortifications of a 2,350-year-old city on Crete marked by extensive signs of siege, Culture Ministry officials said yesterday. The archaeologists discovered the remains of a fortified tower, a city gate and a 3.5-kilometer (2.2-mile) wall surrounding the ancient city of Aptera, near the port of Hania and dating to 4 BC, the ministry said.

Towards the end of the Minoan age, Aptera was at the peak of its development. This belief is supported by the formidable, large stone cyclopean city walls which protected the ancient city. Defense was a major concern of the Apterians, as traditionally they had fierce and powerful enemies.

This retaining wall along a Southern California highway follows the contours of the rolling hills. It retains the soil where it needs retaining and then dips down so as not to obliterate the essential forms of the land. By following the curves rather than imposing an overbearing hard straight line on them, the view is enhanced instead of destroyed.
Photo courtesy of Leslie McGuire

The Romans Rethink Decorative Walls

Instead of a solid wall of bricks or stone blocks, a Roman wall consisted of two outer walls and a cavity in the center filled with rubble and mortar or packed clay. To make them look nice—and probably also solid, facings were added along with a coating of plaster.

Stone walls or facings might also be made of trimmed rectangular stones of irregular sizes, opus incertum. The stones could not be laid in straight courses, but when carefully fitted together with some stones extending deep into the wall or even through to the other side, this pattern made for a very strong wall. These patterns of construction depended on lime mortar to hold the elements together.

Some of the principal doorways in ancient Ninevah were flanked by human-headed bulls. They were also placed at the entrance of palaces as a pair. At the entrance of cities, they were sculpted in colossal size, and placed as a pair, one at each side of the gates to the city. Each bull god looked towards one of the cardinal points.

Concrete Comes of Age

About the third century BCE, Roman builders discovered that volcanic ash, when added to lime mortar, made a cement that cured to a rocklike hardness even under water. Mixed with sand and gravel, this material was the equivalent of modern concrete. At first concrete was used like a particularly durable mortar, or for places where its ability to harden without drying out was important-for the water courses of aquaducts and for bridge pilings, as an example.

Evoking the antiquated style of antiquity, these bricks set in mortar are reminiscent of the combination of rubble and trimmed rectangular stones of irregular sizes, known as opus incertum. The stones could not be laid in straight courses, but when carefully fitted together with some stones extending deep into the wall or even through to the other side, this pattern made for a very strong wall. According to Vitruvius, opus incertum is an “ancient style.”
Photo courtesy of Leslie McGuire

Trickery and Reinforcement

Instead of tricking wandering hoards, now retaining walls trick wandering soil. Ancient people all knew about the necessity of reinforcing soil. Papyrus was used in ancient Egypt not just to make paper but also to trick soil into staying put. Bamboo was used in part of China’s Great Wall.

Retaining walls have diverse functions in the modern world: they can be structural walls to—keep soil from changing grade, give bridge abutments something to hang onto, keep waterfront structures out of the water, keep tunnel access routes from filling in with dirt, keep streams from having an out-of-stream experience (otherwise known as stream channelization), or parking-area support to keep only cars in the lot, not mud.

Vegetation can also make a block retaining wall aesthetically pleasing as well as stronger. The roots of the plants stabilize the soil behind the wall and prevent the fines from trickling away over time. Many walls are topped with hanging or trailing plants, and manufacturers produce blocks that can contain plantings.

And While You’re At It…Bring in Character and Artistry

Just as there is more than one way to skin a cat, there is also more than one way to create a retaining wall. By looking at all the ways the ancients built their walls and decorated them, it is but a short step to add their thoughts to one’s own strategies. By removing defense from the equation, the field is wide open. Add bigger and better planting wells, and throw in a few stream runnels. Create patterns with facings, bas-relief and stencils that mirror or enhance the natural gifts of the locale. Allow the walls to follow the contours of the land, dip and slide with the hills and dance along the curves of ancient paths. After all, the journey is more about the view than it is about the destination.