Originally posted by: Vibhishna
In the translation I read it was not mentioned. I don't think Lakshman Rekha is mentioned in the Valmiki Ramayan.
Lakshman rekha is nither mentioned in Valmiki ramayan nor in Ramcharitramana's aranya kand but the mentioning of lakshman rekha comes in Lanka kanda of Ramcharitramanas
"Mandodari rebukes ravana on his boisterous claims of valour by hinting that his claim of strength and valour is shallow for he could not even cross a small line drawn by Shri Rama's younger brother Lakshmana." (Ramcharitramanas, lanka kanda, 35.1)