Replacing much simpler predecessors, the first more formal, stone built agricultural terraces were constructed in Peru in the middle of the first millennium AD. The most obvious use of these platforms in the hillside is that they counteract soil erosion. But there is more to it than that. By Inca times the technology of the terrace, efficiently watered by irrigation canals, had been perfected. The sophistication of these systems and the effort that went into their construction is truly remarkable.
The stone walls, subtly inclined into the hillside, serve to stabilize the planting platforms. They also absorb heat from the sun during the day and release this nightly, helping to create a slightly warmer internal micro-climate which protects the crop from frosts. The construction of the typical Inca terrace includes a top layer of selected agricultural soil, sometimes brought considerable distances, above unselected, in situ soil and overlying a layer of small stones with larger stones at the base (see diagram). This facilitates drainage and increases the humidity and warmth in the soil, promoting greater microbiological activity. In turn this stimulates rapid germination and plant growth and enhances yields. When irrigated, well built terraces can double the productivity of the land.