How were Roman Forts planned and built?

Upon halting for the night, the famed Roman Legions would erect a castrum--a fortified encampment in which to slumber, and from which the English language gets the word “castle“. Typically castra were built of earth and wood, as they were designed to be broken down the next day. However, when a more permanent military presence was required--such as along Hadrian’s Wall, the timber and earth would be swapped out for brick and stone, like the fort at Vindolanda. The Roman castrum was usually situated on a