A great advantage that rubble walls offered is that when heavy rain falls, their structure would allow excessive water to pass through and therefore, excess water will not ruin the products. Soil erosion is minimised as the wall structure allows the water to pass through but it traps the soil and prevents it from being carried away from the field. One can see many rubble walls on the side of the hills and in valleys where the land slopes down and consequently the soil is in greater danger of being carried away.[citation needed]