Query: what were the walled forts of Fort William in Bengal, Fort St George in Madras and Bombay castle before they were forts?
Context: By 1647, the company had 23 factories, each under the command of a factor or master merchant and governor if so chosen, and 90 employees in India. The major factories became the walled forts of Fort William in Bengal, Fort St George in Madras, and Bombay Castle.