George Lensen's "The Russian Push Toward Japan", 1959, cites Okamoto Ryunosuke, "Nichi-Ro kosho Hokkaido shiko", 1898, to say:
Matsudaira Sadanobu states that guns for defenses must be of bronze. There was a bronze reservoir in Osaka. He suggested that it be replaced by one of stone, and the bronze melted and made into cannons.
Under what circumstances would anyone construct a reservoir of bronze? Is reservoir even the right word here? Was it melted down after all?