The southern boundary between German East Africa and Portuguese East Africa was formed by the River Rovuma, which, coming from the high plateau and the mountains to the east of Nyasa, is one of the large African rivers. Except in its highest reaches near Lake Nyasa it is not fordable, and makes an admirable strategic line. However, as Portugal came into the war after most of the German colony had already been occupied by us, this river acquired strategic importance only toward the end of the campaign, and then in a sense adverse to us, as General Van Deventer has found to his cost. After the remnants of the German native forces had been driven across the Rovuma at the beginning of December, 1917, our forces found the swift pursuit across the river a difficult task. We are, however, now operating against the roving bands into which the enemy force has split, and if ever they try to break back to their occupied colony, they will find the line of the Rovuma a very serious barrier. [Sidenote: The search for the German raider _Koenigsberg_.] [Sidenote: The _Koenigsberg's_ guns accompany the enemy on land.] The eastern boundary of the colony is the coast-line of the Indian Ocean for almost five hundred miles, with some very beautiful harbors, and it was dominated by our navy from the day that war was declared. The Royal Navy has played a very active part in our African campaigns, and one of the most fascinating episodes of the war was the search for the _Koenigsberg_, lost after she had destroyed the _Pegasus_ and done much damage in the Indian Ocean. She was discovered in a most secluded branch of the Rufiji River, and ultimately destroyed by seaplanes and monitors in her impenetrable lair. Yet, though destroyed, she made her voice heard over all that vast country, for her ten big naval guns, each pulled by teams of four hundred stalwart natives, accompanied the enemy armies in all directions, and, with other naval guns and howitzers smuggled into the country, made the enemy in many a fight stronger in heavy artillery than we were. [Sidenote: Extensive enemy fortifications at the mountain gap.] [Sidenote: The rainy season worse than imagined.]