Now you may be wondering, "Whatever would they need petticoats for with a hoop skirt?" Absolutely everything had its purpose.
Usually ladies wore two or three petticoats with their hoop skirts just to soften the silhouette. Here is a picture I got from another blog for this same example:
Now this lady just needs to adjust her hoop, but a petticoat or two would help make her skirt more round.
This is a look you definitely want to avoid. You don't want to be able to see the bottom rung. Reenactors have dubbed this "lampshading", in which the shape of the skirt is like a lampshade and the bottom rung shows.
Here is a picture of what you do want it to look like:
This dress is lovely and round, and you can tell it has a petticoat under it.
Another petticoat that was a must was a small petticoat to go under the hoop. Remember how I told you about the drawers with the split-crotch seam? Can you even imagine if you were wearing a hoop skirt, sat down just a little too far back, oh the horror as your hoop skirt flies up in your face!
To save themselves some embarrassment, they wore less full, short petticoats (knee length) and saved themselves the mortification.
Here are some beautiful pictures I found of originals:
These ones would definitely be worn over a hoop skirt. They loved to make the hem very intricate, even though no one could see them. Don't ask me why! I particularly love the diagonal work in the first one.