In October 844, 80 longships sailed up the Guadalquivir River in the Emirate of Cordoba and besieged Seville, a reach made possible by one technology. The longship’s roots run from Bronze Age Swedish petroglyphs around 1800 BC and the Hjortspring boat of about 350 BC to the Nydam ship of around 320 AD, which introduced clinker building with overlapping planks fastened by thousands of iron rivets smelted from bog ore. Shipwrights split freshly cut green oak with axes instead of saws, choosing naturally curved trees so the fibers stayed intact, and as the green wood dried it pulled tighter against the rivets, sealed with tarred wool or animal hair. The result was a light, flexible hull that twisted with the waves and could float in a meter of water.

The sail, adopted around 780, reshaped Scandinavian society: one 100 square meter wool sail needed about 180 kilometers of hand spun yarn and more than a year of women’s labor, and a spar called the beitass let ships work into the wind. Navigators relied on the sun, the North Star, seabirds, and swells. Thorkild Ramskou’s 1969 sunstone theory is unproven, since no sunstone has been found in a wreck and astronomer Bradley Schaefer found Iceland spar performed poorly in real fog. Longships dominated for centuries until tall Hanseatic cogs made boarding impossible, and in 1429 a Norwegian levy fleet was destroyed by the Victual Brothers.

• The word starboard comes from steerboard, the side where the steering oar was mounted.
• Rigging was made from linden bark or spiral cut walrus hide that resisted saltwater rot.
• A wooden disk found at Uunartoq in Greenland appears to be a sun compass.
• Roskilde 6, from around 1025 AD, is nearly 37 meters long and carried about 100 men, including 78 rowers.
• Olaf Tryggvason’s Long Serpent was a dragon ship with 34 pairs of rowing benches.