Short answer: creosote. It's basically tar made from coal, they soak the wood in it and the tar makes the wood far more durable and waterproof. It's the same r

Short answer: creosote. It's basically tar made from coal, they soak the wood in it and the tar makes the wood far more durable and waterproof. It's the same reason railroad ties can last basically forever. https://en.wikipedia.org/wiki/Creosote https://en.wikipedia.org/wiki/Creosote