Hiram cast two pillars of bronze. Eighteen cubits was the height of one pillar, and a line of twelve cubits measured its circumference. It was hollow, and its thickness was four fingers. The second pillar was the same.
1 Kings 7:15

The bronze pillars of the Temple were massive: 27-30 feet high, 18-20 feet in circumference, and 6-7 feet in diameter. The walls were about 4 inches thick. They were cast from molten bronze, maybe not so difficult with modern technology, but very difficult in 950 BC.