ARX was a type of building block that was used by ancient people called the Romans. These blocks were made out of really hard materials like stone or brick, and they were used to build really tall and strong buildings that could last for a very long time.
ARX blocks were really special because they were designed to fit together perfectly, like puzzle pieces. This made them really strong and durable, and helped the buildings that they were building to stay standing for many years.
In fact, some of the buildings that used ARX blocks still exist today, even though they were built a really long time ago! These buildings are really important and special because they give us a glimpse into what life was like for the Romans many years ago.