Conditions in the Atlantic Ocean could be difficult, with many squalls and regular, violent storms to navigate. Any vessel hoping to survive a voyage in this rough weather needed to be strong and sturdy. The Celts used oak in their ship construction, which meant their hulls could withstand the battering of both the waves and Roman ships, but it also meant they needed a sturdier sail. Leather was the favoured material, it was hardwearing, could cope with rough conditions, and the sheer weight of the ship it was attached to.
