I don’t think Silversea or Seabourn, or any other cruise line for that matter, do Rome or Athens to Dubai or vice versa on a repetitive basis during a season. These are usually are bookable segments of “world” cruises and typically happen in the Med shoulder months either in the early spring or early fall. In our case we were on Silversea’s Spirit in late November/early December and caught her exiting the Med to the east for what would be her partial winter season in the Indian Ocean and western Asia. Even that was a bit of a strange and one-off season as the Spirit made the reverse trip about 80-90 days later. She was coming back into the Med in basically the off season for the Med for an extensive renovation that included cutting the ship in half and adding a 50-foot section.
We did see the Celebrity Constellation at a number of our stops and she eventually was docked behind us in Dubai. Not being interested in Celebrity or any large ship line I didn’t research their itinerary so don’t know where they started, stopped, or how long was the cruise. Actually what struck me at the time was me wondering how they darkened that large ship to get through the Somali pirate zone. On our ship all external lights were turned off except those required for navigation. All the drapes were closed and the decks were basically off limits from sunset to sunrise the next day. Our ship didn’t but I know some cruise lines go as far as to hire SWAT-like security teams for transmitting the pirate zone. We might not have as just before sunset I saw an Indian Navy destroyer take up position a couple hundred yards to our starboard aft. I assume they stayed there through the night but were gone early in the morning.