In the world of boats, there are small boats, bigger boats, and then there are the really big boats, like cruise ships. The MSC Meraviglia, built in Saint-Nazaire, France and in service since 2017, is the biggest cruise ship to have ever docked in New York City. It has a water park, a rope course, a spa, a mall, an arcade, a bowling alley, a casino, a gym, two theaters, five pools, nine restaurants, 23 bars, 19 floors, and enough room for 5,655 passengers and 1,536 crew members.

Cruise ships are the biggest passenger vessels that humans have ever built, and they have a certain look to them that is far from the look of the big transatlantic ships of 100 years ago. So how did the biggest ships we build wind up looking like this?

Before cruise ships, the biggest ships on earth were ocean liners, designed for one purpose: to take you somewhere. In the golden days of ocean travel before the airplane, people had no choice but to use ships. Advertisements from this golden era of ocean liners boasted their speed across the Atlantic and their luxurious comfort, which, given the conditions on the open ocean, wasn’t always easy to achieve. To inspire the confidence of passengers, ocean liners like the RMS Aquitania were designed to look like great palatial hotels or even palaces themselves, with restaurants, smoking rooms, gardens, and a massive lounge with painted ceilings.

However, the rise of air travel meant that ships stopped being the only way to cross oceans, and by the 1960s ocean liners were slowly becoming obsolete. As ocean liner companies struggled to sell tickets, they tried something different: they started advertising ocean travel as a vacation, and the cruise ship was born. But it wasn’t until the TV show The Love Boat that cruising became mainstream.

Ocean liners had a problem, though. They were designed to go fast and consumed a lot of fuel, they sat low in the water, and they had separate sections for first, second, and third class, which limited everyone’s freedom of movement throughout the ship. And compared to the full time cruise ships of the time, ocean liners were huge, so they’d have to attract a lot of vacationers to be profitable. Everything that had made ocean liners optimally designed for commuting quickly through rough waters made them poorly fit for vacationing slowly through calm ones. The SS France, which was the largest ocean liner in the world, could not generate enough revenue to operate and sat idle for years until 1979 when Norwegian Caribbean Lines purchased it and announced they would convert it into a full-time cruise ship. To make the ship more accessible to passengers, they shut down one engine room and removed two of the four propellers, installed tenders to get passengers to islands without deep ports, and took out the barriers between class sections. To attract vacationers, they loaded the ship with a massive roster of entertainment options, including sporting facilities, shopping centers, cinema, bars, a multi-confession church, saunas, kindergarten, party games, educational courses, library, and charades.

The ship began service in 1980, renamed the SS Norway, and made only two stops in a weeklong cruise. This was because the ship was the destination itself, and it proved that size worked for cruise ships and kicked off a race to build bigger and bigger ships, changing the look of cruise ships forever. To fit more cabins and amenities, the superstructures became taller, hiding the once prominent smokestacks, and wider, shortening the bow and eliminating open deck space. The Norway was the biggest operating passenger ship in the world with an internal volume of over 70,000 gross tons, but the ships built over the following decades made it look tiny. The Queen Elizabeth of 1940, which held the record for so many years, was 83,000 tons; however, the new Royal Caribbean ships are literally three times the size. The Icon of the Seas, launching in 2024, will have a volume of over 250,000 gross tons.

Currently, there are over 320 cruise ships sailing around the world, but the only ocean liner left is the Queen Mary 2, built in Saint-Nazaire, France and christened by Elizabeth II in 2004. It is still in regular service from Southampton to New York City.