King Ezana of Aksum, in present-day Ethiopia and Eritrea, adopted Christianity under the influence of Frumentius, making Aksum one of the first Christian states.
Emperor Constantine I dedicates Constantinople as the new capital of the Roman Empire.
In the desert of southern Peru, the Nazca and earlier cultures create enormous geoglyphs on the ground, best seen in full from above.
Teotihuacan in the Valley of Mexico grows into one of the largest cities in the world of its time, with the Pyramid of the Sun and the Avenue of the Dead.
Maya city-states such as Tikal, Palenque and Calakmul reach their height in architecture, writing, astronomy and calendrics.
The Soninke Ghana Empire (Wagadu) flourished in what is now Mauritania and Mali, growing rich from control of the trans-Saharan gold and salt trade.