There have been hundreds of trends that have come across Geometry Dash over the years. From 1.0 styled levels, to level remakes, to even levelution, Geometry Dash has seen so many popular trends. But there's one trend that stands above the rest in terms of how much of an impact it has had on the community, and that trend is the Nine Circles trend.
The trend started with the original Nine Circles by Zobros. It was released January 17th, 2015, and while it may not be the best level out there, the important thing is that this started the trend.

The next Nine Circles level to be released was not in fact Fairydust, but it was in fact Beautiful Eyes by TGirl (the ID for Beautiful eyes is 4913027, while the ID for Fairydust is 5310094). However, it wasn't very good, so let's forget about it. Fairydust was the next level to come out, although it was really just a recolored Nine Circles, with lots of parts clearly being outright recreations of parts of gameplay from the original. From then on, everyone started making their own Nine Circles levels, ranging drastically in difficulty, color scheme, music, and style.

There were different variations of Nine Circles levels that were made, such as the Ultra style (levels include Ultra Paracosm and Ultra Fairydust), the XII style (levels include Nine Circles XII and Paracosm XII), and the modern style (includes levels such as Arctic Lights, Hyper Paracosm, and Bausha Vortex).

Despite all the variations, normal Nine Circles levels were still being made, such as Solar Circles, Infinite Circles, and Crimson Clutter. It got to the point where community icon Andromeda created his own Nine Circles level called Poltergeist. This was one of the hardest levels in the game and was the hardest Nine Circles level at the time. That is, until Cyclic created his own Nine Circles level, the infamous Sonic Wave. There were two versions, the original light blue version, and the newer dark blue version. Both versions were hacked, and Sonic Wave was left without a verifier. It stayed like this until some people decided to try and be the first to complete it. Eventually someone named Mefewe started getting some great progress, and ended up getting 98%, dying to his own buff.

Once that happened, he got some people to create a rebirth of Sonic Wave titled "Sonic Wave Rebirth."

However, before those plans could be finished, someone named Sunix came out of nowhere and completed Sonic Wave on stream, becoming the first legit victor. Sonic Wave instantly took the #1 spot on the demons list, and is still in the main list today. At this point, the Nine Circles trend was still going strong. That was, until 2.0.

2.0 was a pretty weird time for Nine Circles levels. While some did take advantage of the new features of the update, such as Crying Souls, Quasar, and Ultra Paracosm, most levels stuck to the classic formula. And in fact, it was this update that gave rise to one of the most famous Nine Circles levels ever created. On October 3rd, 2015, ToshDeluxe released a video on a level titled "Silent Circles." It was a collaboration between Cyrillic and Sailent, an old creator famous for his silent levels. This level was famous not just because of the fact it was a Nine Circles level, but because of the unique way it was impossible. Around the halfway point, you encounter an extremely tight mini wave spam that is humanly impossible, and this was what made Silent Circles so famous.

Other than that, 2.0 didn't see very many famous Nine Circles levels get released. 2.1 came around, and while levels such as Arctic Lights, Hue Effect, and Bausha Vortex have been released, it's safe to say that the Nine Circles trend is dying out. Or at least, it was dying. Nowadays we've seen a resurgence in the Nine Circles trend.

Several popular Nine Circles levels have come out in recent times, enough to make it seem like the trend has been revived. From the revival of Sonic Wave Rebirth, to the release of both Sonic Wave Infinity and Cosmic Cyclone, to even the current verification of the Silent Circles remake, the Nine Circles trend has thrust into the spotlight yet again. All this has made it clear that despite the fact the original Nine Circles came out over 7 years ago, the trend isn't going to be dying anytime soon. I personally can't wait to see what the future of this trend has in store.