The most economical definition of wealth in ancient philosophy may be the one offered by Epicurus in his Vatican Sayings: "Natural wealth is both limited and easily acquired; the wealth defined by groundless opinions has no limit." The sentence is nearly a proof. If wealth means having more than you want, then the path to it forks: accumulate more, or want less. The first path has no natural ceiling. The second one does — and that ceiling is where most people could actually stop.
Epicurus made this concrete in a way his reputation doesn't always suggest. He lived in a garden in Athens with a small group of friends and students. The diet was simple — bread, olives, water, occasionally cheese. This is often presented as asceticism, but his own framing was the opposite: he was rich. In the Letter to Menoeceus, he addresses the charge that his philosophy condemns pleasure: "When we say that pleasure is the end and aim, we do not mean the pleasures of the prodigal or the pleasures of sensuality, but rather the absence of pain in the body and of trouble in the soul." The pleasures he was after — friendship, conversation, quiet — were not expensive. They were available. The desire for things beyond these categories was what made them seem otherwise.
The key move in Epicurean thinking is a taxonomy of desire. Natural and necessary desires — food, shelter, companionship — are satisfiable; sating them produces genuine relief. Natural but unnecessary desires — fine food rather than adequate food, a larger house rather than an adequate one — are satisfiable but not essential to satisfy. Empty desires, whose object has no natural limit (fame, wealth accumulated as an end in itself), are never satisfied because satisfaction was never the mechanism. The wanting runs on itself. A third luxury item doesn't produce twice the ease of a second. The anxiety about not having enough returns quickly regardless of how much arrives.
Seneca, in Letter 17, gets at the same problem from a different angle. He suggests an experiment: set aside several days to live on the simplest possible food, coarse clothing, the barest necessities — and ask yourself afterward, "Is this the condition that I feared?" The exercise isn't austerity as punishment. It's austerity as information — a test of what the anxiety was actually about, and whether the feared simplicity was as fearful as advertised. Most people who do this find that the feared life is manageable. Often more manageable than the one spent avoiding it. In Letter 16, Seneca makes the same point more directly: "It is not the man who has little who is poor, but the man who hankers after more."
What links Epicurus and Seneca here is a practical curiosity about the gap between what imagination promises and what experience delivers. The desire for more projects itself into the future as a solution to a present dissatisfaction. But the dissatisfaction usually has a cause that more won't address. The next thing arrives, and the background feeling persists — because the background feeling was never really about the thing.
The Epicurean question is a useful one to return to: of the things that seem necessary right now, how many are natural and how many were acquired through habit and comparison?