The earth, 土 tǔ, embraces all of nature.
Yet it is represented in the most minimal form in this ideogram containing the character of ten ‘十,’ which in Chinese also means ‘complete’, suggesting the richness of earth. A vertical line below indicates ‘earth’.
The earth, developed by man. Hence the creation of cities. And so, by adding ‘grown-up 成’ to the character ‘土’, we have ‘city 城’.
Some say the ancient script resembling a poop. Could it be as simple as that?