Marble is a Resource available in the Bronze Age. It is unlocked by researching the Stonecutting Knowledge.
Marble is a rare resource, rarely found in the mediterranean climate only. Like Stone blocks, it requires a stonecutter's annex, the quarry, to gather. Stonecutters can also gather Stone, and stone blocks from marble.
Marble is a vital late game resource. It is needed for most Iron Age government buildings, including the City Hall. 30 Marble is needed for each building, so securing a source or trading rights with a nation with a source is vital for advanced civilizations.