A monitoring system for a periphery of a structure comprises a monitoring module (102) having a detection and ranging system (304, 308) arranged to support monitoring of a portion of the periphery corresponding to a coverage field in order to detect passage of a body beyond the periphery. The detector (304, 308) has an imaging resolution that prevents conclusive visual identification by a human operator of the nature of the body. The monitoring module also comprises a video capture apparatus (312, 314) arranged to provide video data in respect of the coverage field. The system also comprises a monitoring station apparatus (200) arranged to receive data from the monitoring module (102). In response to detection of the passage of the body by the detection system (304, 308), the monitoring station (200) enables the operator to review the video data. The video data enables the operator to identify readily the nature of the body detected and thereby to provide confirmatory visual evidence when the body is human.