The striking figure of the Powder Gate is one of the most distinctively Czech sights in Prague. It has served as an entrance into Old Town (Stare Mesto) since the 11th century, but the gate you see now was begun in 1475 and modelled on Peter Parler's tower that sits on the Old Town side of the Charles Bridge.
It is called the Powder Tower because it was used to store gunpowder in the 17th century. Walking through its gate you cross between Old Town, established as early as the 11th century, and New Town, established by Charles IV in 1348.