Retaining wall 60 cm high - foundation necessary?

I would use at least 20cm of concrete, better 30cm. Then you can also save yourself the backrest.

Alternatively, the mentioned dry stone wall. But then with different stones and with a backward slope.

Also an idea, then I could stick to 20 cm width. 20 cm mineral and 30 cm concrete. At a width of 20 cm, it is not expensive. That’s a plan without [rüxkenstütze].

I would take at least 20cm of concrete, better 30cm. Then you can also skip the back support Alternatively the mentioned dry stone wall. But then with different stones and sloping backwards.

So you mean excavate the humus layer and vibrate the sand once and then pour 30 cm deep 20 cm wide screed concrete, after drying set the wall stones in lean concrete without support? Regards

You can actually omit the lean concrete. Just set the stones in a thin mortar bed. For that, vertical reinforcing bars in the foundation that connect it with the stones. And also a bar in the stones to connect them with each other. Then it should hold well.

Okay, that means a 20x40 foundation with one layer of reinforcement in the foundation (every second stone should be enough?), and set the first row in masonry mortar. Since we might want to put a 1.40 fence on top later, up to where should the stones be concreted? Or fill it completely and drill later?

Ideally, you should concrete the fence posts in right away. Otherwise, I would fill it and drill later. For the irons, I would do one iron per half brick each, they’re not that expensive. But at that height, you can certainly save and do fewer.