plural names of cities

[benissimus]

Is it known why the names of many prominent cities in Greek and Latin are plural nouns? e.g. Ἀθῆναι, Δελφοί, Θῆβαι, Cannae. Under the heading for Ἀθῆναι, my Lewis & Scott says:

used in pl., because it consisted of several parts

That seems really unlikely to me. Is there a consensus on this?

[swiftnicholas]

This doesn't solve anything, but here is what Smyth (1005) says:

"Names of towns and parts of the body are sometimes plural: Ἀθῆναι, Athens, Θῆβαι, Thebes, στήθη and στέÏ￾να, breast (chiefly poetic). The name of the inhabitants is often used for the name of a city: Δελφοί D.5.25."

Right after this he talks about the plural being used to lend dignity. The LSJ says the same thing about being composed of parts.

[IreneY]

Well that's what I was taught, at least for Athens (can't remember about other cities). Many little settlements that became one big city.