Rats were only a problem for those who didn’t eat rats. But the Romans kept dogs, and they were experts at building stuff; as have many people, the Roman basically stuccoed their exteriors to cover up any holes or the mortar lines between the stones or bricks. Then they’d paint the whole thing. Over the intervening years, the plaster crumbled off, but is still seen on houses and whatnot in Pompeii and the other towns buried by Vesuvius. Grain storage was probably kept dry and safe from the rats using a stucco finish.
The underlying brick now looks like the market of Trajan:
https://www.google.com/search?q=market+of+trajan&tbm=isch
Grain was shipped, I suspect, directly in the hulls of those ships; I’ve guessed this because of the way those ancient wrecks are found with all the amphorae intact, despite the fact that they often had pointed ends. The point makes sense if they were loaded in and burrowed down into the grain. After 2000 years on the bottom, the grain is long gone (assuming it didn’t just float up and away) and the amphorae are all still there, unbroken despite their trip to the abyss.
“The underlying brick now looks like the market of Trajan”
The first shopping center. I wonder if they had a Macy’s. I’d shop there; matter of fact, I’d shop anywhere. Female perogative.