ろ seems to be a common imperative conjugation of verbs.
なさい seems to act in a similar way (maybe not so demanding) but it is also described as an imperative form:
do ... (usually written in kana) (imperative form often used after the -masu stem of a verb) (see also: なさる)
Whats the difference between ろ and なさい?
For instance we can have 食べろ and 食べなさい - how do they differ?