This broad, gently curving stretch of water represents a segment of the great inner moat of Edo Castle. The red-gated mansion to the upper left belonged to Ii Naosuke, one of the shogun's closest political advisers. It was along the road to the lower left that he was assassinated by a group of hotheaded young loyalist samurai as he proceeded from his mansion to Edo Castle on a snowy day in early 1860.