I'm perhaps a prison for those who commit no crimes I'm similar to a circus but have no mimes Between are bars, one side spends life, the other spends time I'm not so joyous when you notice all the grime

Y’arrrr me leg be gone but still. A wooden post now fits the bill. What what is this thing that keeps me steady?

When one door closes, I come knocking. Some people catch me, some people let me slip. I’m hard to find. I’m hard to make. I’m taken for granted when fear takes place.

The first word is only three letters, but the definition is always questionable. Some wonder if life imitates it or does it imitate life? The second word is four letters long defined as a thing that is proven or known to be true. I will be in the middle of these two words and make a word that means a man-made object, tool or relic.

A word I know, six letters it contains, remove one letter and twelve remains. What is it?