Reddit’s AskHistorians section discussed the history of flag design:

• Ships used to fly flags to show what country they were from. A rectangular flag catches the wind the best.
• Soon the idea of flags being used to represent countries at sea turned into flags being used to represent countries in general.
• European colonialism then spread this idea to the rest of the world.
• There are exceptions. Nepal’s flag has a non-rectangular shape because it’s based on the royal standards of its Kings.
• The Swiss flag is a square because the flag is based upon its military colours which across Europe are usually square.
• The Swiss naval flag, however, is rectangular.

Read the entire discussion here and see what flags in the past used to look like.

Source: Reddit