An ancient type of chain, from c. 2500 BC, of which the links are initially of oval shape and are bent back against themselves so as to form a U-shape, after which each link is threaded through thelooped end of the preceding link, resulting in a somewhat square section (hence sometimes called a 'square chain').A more compact variation is the 'double loop-in-loop where each added link is slipped through the loops of the two preceding links. The last link of each such chain is closed by soldering. Some suchchains are made broad by cross-linking two to eight basic chains.