Some study of the map of the scene of battle is necessary for a perfect understanding of the movements of the contending forces. It will be seen on reference to our map (page 169) that just above Wiju the waters of the Yalu are joined from the northwest by an important tributary, the Ai River, the stream here taking the form of a fork. At the apex of the triangular wedge of land which divides the Ai from the Yalu is situated the Hosan, or Tiger Hill, an important strategical position commanding the south bank of the main river. Opposite Tiger Hill, and running some way past it up the Yalu, is the Island of Kulido, which divides the river at this point into two streams, both of them fordable. The Ai also is fordable at a point near the hill of Yulchasan, which is north of Tiger Hill and on the same bank of the tributary. Opposite Wiju itself the main river is two miles wide and is divided into three streams by two islands. Of these the larger Cheun-song-do, is near the right bank, and lies stretched alongside it for a distance of about thirteen miles, starting from a spot close to Antung, lower down the river, and finishing at a little distance up the Ai. It can be reached from the right bank at this end by a ford, and there is another ford lower down, opposite to Chiu-lien-cheng. The stream dividing the other island from the left bank is also fordable waist-deep, but the central stream can only be crossed by means of a bridge. These islands are really low, flat, sandy deltas, with occasional clumps of small trees and patches of shrub dotting their surface, which provide some cover for the concealment of troops. [Illustration: MAP SHOWING THE ACTIONS ON THE YALU APRIL 29TH-MAY 1ST.] [Sidenote: General Sassulitch's Defences]