Medallion Architecture
also called Bronze Silver Gold, Multi-Hop Architecture
Layering a data platform into raw, cleaned and business-ready zones so that reprocessing is always possible and quality improves in defined steps.
The layering exists to answer one question well: when a transformation turns out to be wrong — and it will — can you reproduce every downstream table from something you still have? Keeping the raw landing zone immutable is what makes that a yes.
Bronze is source data as it arrived, append-only, schema-on-read, with ingestion metadata. It is deliberately ugly. Silver is cleaned, conformed, deduplicated and typed, with keys resolved and business entities recognisable. Gold is shaped for consumption — aggregates, dimensional models, feature tables — and is where most query volume lands.
The failure mode is treating the three names as a mandatory ritual rather than a design principle. Small platforms end up with three physical copies of data that needed one transformation, paying triple storage and triple latency for ceremony. The layers should exist where there is genuinely distinct work being done at each.
The other trap is quality checks placed only at the end. Validating at the bronze-to-silver boundary is what stops a malformed source file from silently poisoning forty downstream tables, and it is far cheaper than discovering it in a board report.