The hippocampus is divided into several subregions, such as CA1, CA3, and the dentate gyrus. In addition to these subregions, a structure called the fasciola cinereum (FC) has been reported to exist in the hippocampus. However, this area has received little attention, and been poorly studied due to its small size (0.1 mm in width). In this study, therefore, we conducted the first study to ever report basic properties of the FC, ranging from its genetic and anatomical features to its physiological and functional signatures. The FC had a completely different genetic profile from the neighboring CA1, demonstrating that the FC is an independent hippocampal subregion. Anatomically, the region mainly projected to the dentate gyrus of the hippocampus, which is a unique property among other hippocampal subregions. To understand its functional role, we lesioned the FC and tested memory performance during contextual memory task. Lesioning the FC impaired the acquisition of new contextual memory whereas the retrieval was intact. Physiologically, we reported a smaller fraction (33%) of place cells in the FC that were indistinguishable from those in CA1 in terms of basic properties. However, place cells in the FC fired only transiently in their place fields. These transient firing patterns of the place cells in the FC may play a critical role in learning a novel contextual environment by facilitating the temoporally structured contextual pattern separation in the DG of the hippocampus.