Herein we present the first straightforward aryne polymerization that successively connects aromatic rings at their ortho-positions, directly giving poly(ortho-phenylene)s of up to ca. 100-mer size. The polymerization proceeds smoothly in a chain-growth fashion in the presence of a monovalent copper reagent. Direct synthesis of poly(ortho-arylene)s has been a "missing piece" of aromatic chemistry for a long time (although the discovery of arynes dates back to 1902), in contrast to the well-investigated para- and meta-linked polyarylenes. Our achievement reported here is expected to open up new areas of nanocarbon and materials science.