Map of Tarawa atoll, 1873Chance visits by European ships occurred in the 17th and 18th centuries, while those ships attempted circumnavigations of the world, or sought sailing routes from the south to north Pacific Ocean. A passing trade, whaling the On-The-Line grounds, and labour ships associated with blackbirding of Kanakas workers, visited the islands in large numbers during the 19th century, with social, economic, political, religious and cultural consequences. More than 9,000 workers were sent abroad from 1845 to 1895, most of them not returning.