If you are putting an urban bench on bare soil, the foundation choice comes down to how permanent you need the bench to be and how much frost or rain your area gets. The most common recommendation is a concrete footing pad under each leg or mounting point. Dig a hole roughly 12 inches deep and 10 to 12 inches wide, pour 4 to 6 inches of compacted gravel at the bottom for drainage, then fill the rest with concrete. Set an anchor bolt or post base into the wet concrete so the bench can be bolted down later. This stops the bench from sinking into soft ground and keeps it level over time.
For lighter benches or temporary installations, a compacted gravel base works well. Excavate a shallow area about 4 to 6 inches deep, fill it with crushed stone or decomposed granite, and compact it in layers with a hand tamper. The bench can sit directly on this pad or be secured with long landscape screws driven through the feet into the gravel and soil below. Gravel drains water away from the bench legs, which reduces rust and wood rot, but it does not prevent gradual tilting as well as concrete.
Another solid option is a ground anchor system. Screw-in earth anchors or helical piles are driven into the soil at each bench leg location. The bench frame then bolts to the anchor plates. This is faster than pouring concrete and works well in clay or sandy soil where you want to avoid digging deep holes. However, it is less effective in loose, rocky, or highly expansive soil.
Whatever foundation you choose, always check your local frost line. In cold climates, the bottom of a concrete footing should extend below the frost depth so the freeze-thaw cycle does not lift the bench out of level. For a standard 6-foot urban bench on soil, two people can usually install a gravel base in one afternoon, while concrete footings need at least 24 hours to cure before mounting the bench. If you are installing several benches along a walkway, concrete footings give the most consistent long-term result, but ground anchors are often cheaper and easier to adjust later.