The city of Rome was (supposedly) founded on this day in 753 B.C. by twin brothers Romulus and Remus. Just to get it out of the way, this most certainly did not happen, as will become obvious as we share the details of the story. Supposedly, the twins were conceived in a fling between the god Mars and the daughter of an ousted king. Her uncle (the new king) ordered the twins to be drowned to prevent them from deposing him. This obviously did not work.
The kids floated down the Tiber River, before being found by a wolf who suckled them until a shepherd came across the babes and took them in. Once grown, the twins attacked and slayed their great uncle. The twins went back to where the wolf came across them and founded Rome there, before entering their own royal spat, which led to Remus' killing at the hands of Romulus.
Skipping forward a bit, Rome started to grow by absorbing other nearby communities. Six kings followed Romulus, the last of whom was a tyrant deposed by a popular revolt. The Romans then got together to form the Roman Republic, which lasted from 509 to 264 B.C.
Is this actually how it went down? Almost certainly not! The Romans didn't start writing down their own history until hundreds of years later, so we'll never really know what happened and when. It's held that there are some general truths behind the story, but we'll never know how much was fact and how much was fiction.