The islands were first populated in larger numbers probably at the time of the Cromwellian conquest of Ireland in the mid-17th century, when the Catholic population of Ireland had the choice of going "to hell or to Connacht". Many fled to the numerous islands off the west coast of Ireland, where they adapted themselves to the raw climatic conditions, developing a survival system of total self-sufficiency. Their methods included mixing layers of sand and seaweed on top of rocks to create fertile soil, a technique used to grow potatoes and other vegetables. The same seaweed method also provided grazing grass within stone-wall enclosures for cattle and sheep, which in turn provided leather, wool, and yarn to make hide shoes, handwoven trousers, skirts and jackets, hand-knitted sweaters, shawls, and caps. The islanders also constructed unique boats for fishing, building their thatched cottages from the materials available, or trading with the mainland.