dear friend, if u have read ramayana it must be known to u that lord Ram was the human encarnation of lord Vishnu, so he has followed the rules of human body. it is almost like todays US and India, US have good technology like Ravan so he became successful to flew with mata Sita, but Lord Ram was like todays India who did not had good technology therefore had to build the bridge therefore took time to reach Lanka. Now this doesnot shows the greatness of Ravan rather it shows the greatness of his engineeres.
