रक्षायन्त्राणि — Military and Defensive Devices

Most of the machines in chapter 31 of the Samarāṅgaṇasūtradhāra are made for royal pleasure, but a small group serves security and war. This article collects them: an iron vessel of heated mercury that roars like a lion and drives war-elephants to flight (31.99–100); armed wooden figures that guard a doorway and strike down thieves at night (31.106–107); and a closing verse that names bows, śataghnīs and other devices "for the protection of the fort", alongside devices for the king's play, as all arising from the right combination of qualities (31.108). The material is brief, and the chapter gives no constructions. To read it properly, the article places it beside the fuller list of fixed and mobile war-machines in Kauṭilya's Arthaśāstra (2.18), the classical Indian source on the subject. Read in modern terms, Bhoja's defensive devices fall into three classes: acoustic deterrents, triggered traps and missile engines. The article examines the feasibility of each, notes the ethical character of the lethal guardian, and explains why a treatise on architecture includes war-machines at all: the fort and the palace were the architect's responsibility. Article 11 of the series Yantravidhāna Studies (SSD-31), on chapter 31 of Bhoja's Samarāṅgaṇasūtradhāra. Verses discussed: 31.99–100, 31.106–108. Web version: sanskritmanthan.in/a/ssd-31-11-raksha-yantra