Back in Marseille, it’s still possible to swim in the late reaches of October. The water, not being oceanic, stays warm, and like the temperature during a clear day, is most invitingly turgid at four in the afternoon. The Mediterranean, being a land surrounded sea, warms up in strata in the spring. In March, the surface to about six inches deep contains the sun rays and is at least ten to fifteen degrees warmer than what lies below.