My shul building is about 80 years old. The aron is huge and holds 10 Sifrei Torah arranged on 2 rows. The back row is higher than the front one.
I noticed that all the "older" shuls that have a multi-row aron have one row higher than the other. I assume that this is mainly for practicality so that you can easily reach a Torah from the back row if you need it. But, I'm curious if there is any halachic prohibition of storing Sifrei Torah in an Aron one directly behind another one?
As I mentioned, it's not practical. However, I believe that one of the Bobover shuls in Boro park has an "elevator" Aron. I.e. the two rows are connected to a chain so that pulling the chain raises or lowers a row (i.e as one ascends, the other descends.) Technically, it is possible for them to have the two rows placed on the same level.