The Ishtar gate was one of the inner gates of Babylon, decorated with animals in yellow on a blue background.
"It [Babylon] lies in a great plain, and in size it is such that each face measures one hundred and twenty furlongs, the shape of the whole being square; thus the furlongs of the circuit of the city amount in all to four hundred and eighty. Such is the size of the city of Babylon, and it had a magnificence greater than all other cities of which we have knowledge. First there runs round it a trench deep and broad and full of water; then a wall fifty royal cubits in thickness and two hundred cubits in height: now the royal cubit is larger by three fingers than the common cubit. [...] In the circuit of the wall there are set a hundred gates made of bronze throughout, and the gate-posts and lintels likewise."
Herodotus - The History I 177-179
Translated G. C. Macaulay