September 15 is the 258th day of the year in the Gregorian calendar, with 107 days remaining until the end of the year. It is known for various historical events, including the signing of important treaties and the birth of notable figures. In many countries, September 15 is celebrated as Independence Day or National Day. For example, Costa Rica, El Salvador, Guatemala, Honduras, and Nicaragua all commemorate their independence from Spanish rule on this date, marking a significant moment in their national histories.