Lead is Saturn. The symbol is a scythe crossed by a bar, and the metal is routinely called Saturn in alchemical Latin; its compounds are saturnine preparations, and saturnism was the standard clinical term for lead poisoning well into the twentieth century.
The correspondence is one of the clearest of the seven. Saturn was the outermost and slowest of the classical planets, taking about twenty-nine years to return to its starting point, and it carried the astrological character of heaviness, cold, age, melancholy and limitation. Lead is the heaviest of the seven metals, dull, soft, cold to the touch and unresponsive. In the hierarchy of metals it sits at the bottom, the base metal against which gold is the perfected one, and it was the standard starting material for transmutation precisely because it was furthest from the goal. Saturn is the god of time and of endings, and lead is where the alchemical process begins in darkness, in the stage called the nigredo.
The word saturnine still means gloomy, and it comes from this system rather than from anything about the metal.
Lead is genuinely ancient. It smelts easily from galena, its sulfide ore, at temperatures a simple fire can reach, and galena also carries silver, so lead was often a by-product of silver production. Lead beads and objects date from the sixth millennium BCE. Its softness, low melting point and resistance to corrosion made it useful for pipes, sheeting, seals, weights and vessels everywhere it was available.