Lead tiles

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"The reason for that is not only that they are fireproof, but also that in times of siege, the tiles could be melted down and cast into bullets."

This has never actually been verified. There are no period sources that support the idea. The real reason lead was used is not completely known, but one plausible reason is that lead (these are simply thin sheets of lead on wooden forms) was lighter than clay tiles in a region where thick heavy snow is common.