You walk past the retaining wall and the wall is holding the hill and the holding is the wall's entire life. The retaining wall does one thing. The retaining wall holds. The hill behind the wall wants to slide and the sliding is gravity and gravity is patient and gravity never stops pushing and the retaining wall never stops pushing back. The retaining wall is the argument between the earth and the engineer and the argument has been going on since the wall was built and the argument will continue until one of them wins and one of them always wins and it is always the earth. Eventually. But the eventually can take centuries and the centuries are the retaining wall's victory.

The Romans built retaining walls with pozzolanic concrete made from volcanic ash and the ash is still holding two thousand years later. The terraces at Pompeii held back the slopes and the holding back survived the eruption and the eruption buried the city and the buried city was excavated and the retaining walls were still standing because the retaining walls were built to outlast everything including the volcano that made the ash that made the concrete. The Romans understood that the retaining wall is not a wall at all. The retaining wall is a negotiation with the earth and the negotiation requires respect and the respect requires engineering and the engineering requires understanding that the earth is heavier than you think and the heavier than you think is the first lesson.

Robert Smithson drove through Passaic New Jersey in nineteen sixty seven and saw the retaining walls along the Passaic River and the seeing was art criticism. Smithson called them monuments. The retaining wall as monument. The retaining wall as sculpture. The retaining wall as the landscape arguing with itself and the arguing made visible in concrete and stone. Smithson understood that the retaining wall is the most honest structure in any landscape because the retaining wall shows you the force. You cannot see gravity but you can see the retaining wall leaning against gravity and the leaning is the evidence. The retaining wall is gravity made visible and the visible is the art even if no one in Passaic New Jersey thought it was art.

In Pittsburgh the retaining walls hold the city together. Pittsburgh is built on hills and the hills are steep and the steep requires walls and the walls are everywhere. There are more retaining walls in Pittsburgh than in any other American city and the more than any other is the geography. The rivers carved the valleys and the valleys made the hills and the hills made the walls necessary and the necessary is the city's skeleton. You remove the retaining walls from Pittsburgh and Pittsburgh slides into the three rivers and the sliding into the rivers would take about ten minutes. The retaining walls in Pittsburgh are not decoration. The retaining walls are the city's argument against its own geography and the argument is expensive and the expensive is why the retaining walls crack and the cracking is the budget and the budget is never enough because the earth does not wait for appropriations.

You see the retaining wall that has failed. The wall has cracked and the crack has widened and the widening has let the earth through and the earth through is the slow avalanche. The slow avalanche takes years. The wall bulges and the bulging is the warning and the warning goes unheeded because the retaining wall is invisible until it fails. No one looks at the retaining wall. No one maintains the retaining wall. No one thanks the retaining wall. The retaining wall holds the ground you walk on and the ground you walk on does not know it is being held and the not knowing is the retaining wall's condition. To hold without being seen. To push without being thanked. To keep the hill from becoming the road and the road from becoming the river and the river from becoming the disaster. The retaining wall. The most necessary thing no one has ever loved.