ALTENA, or ALTONA, a sea-port town of Germany, in the duchy of Holstein, in Lower Saxony. It is a modern town, built by the king of Denmark, and was burnt by the Swedes in 1712, but has since been beautifully rebuilt. The number of inhabitants is about 30,000, and it has a considerable trade. Long. 10. 0. E. Lat. 53. 51. N.