Romulus began to build a wall around the Palantine hill.
I am building the city on Palantine hill!
At one point, Remus jumped over the wall to show how easy it was to get across... which was a bad idea. Romulus became angry and killed Remus.
See? It is too short!
With Remus dead, Romulus continued to work on his city. He officially founded the city on April 21, 753 BC, making himself king, and naming it Rome after himself. The city grew and prospered. For over 1,000 years Rome would be one of the most powerful cities in the world.