The Forbidden City is where the Emperor, the Empress, and many of the hundreds of Concubines lived back in the Dynastic ages.
It was called the Forbidden City because apart from staff, common people were Forbidden to enter.
It is an impressive scale, and seems mostly to be defensive, until you get right to the centre where the living quarters are. The paving stones you see on the ground everywhere go 15 layers deep in a criss-cross formation to prevent marauders from tunneling under and into the courtyard.
The large colanders you see were used to store water in case of fire, and are all over the Forbidden City. Of course, they have sprinklers now, so they lye empty. They were raised in stone with a gap in order to burn a fire below them in winter to prevent the water turning to ice, as it can get as low as -20°C in a cold Beijing winter.
The small creatures you see on the up-turned eves (which, incidentally, are up-turned to allow more light into the buildings) represent the importance of the building and, therefore, how wary anyone should be before blundering in! They are mythical beasts led by a human, and chased by a dragon. There can be from one to 10 (excluding the human and dragon), with 10 being reserved for the most important buildings.