Digital Reconstruction of the Ishtar Gate, largest of the 8 gates of Babylon (now in modern-day Iraq), built approximately 2500 years ago during reign of Babylonian King Nabuchadnezzar II.
Since the star of Ishtar, the goddess of love and beauty, is 8-pointed, the city of Babylon was also built with 8 gates. Because Ishtar's eyes are blue, the door is also blue.