1. Ramayan was written by Valmiki, who also took care of Luva, Kusha and Sita; so it can be aptly called Rama's biography.
2. All the places mentioned in Ramayan, like Ayodhya, Kishkindhya, Lanka are traceable, with unique identity. So it lends credibility
3. Bharata's journey from Kekaya (now in around Pak) to Ayodhya (UP) is mentioned as crossing 3-4 rivers, in the sequence they are today geographically.
4. Saraswati river is mentioned, which vanished 4500 years ago. So Ramayana is at least 5000 years old.
5. Several events (including Rama's birth, Bharata's birth, Rama's coronation, Vali badha, Hanumana finding Sita in Lanka, Army march, Meghanada badha) have been described with the star-pattern in sky at that time. Putting that in "Planetariam" software, gives exact date and time of those events.
6. Rama's birth date comes out as 10 January 5114 BC. Bharata's date comes as 11 Jan 5114. Ramayana mentions Bharata was born 16 hours after Rama.
7. Rama's coronation date comes out as 4 Jan 5089 BC. Ramayana mentions Rama was 25 years old while being coronated. Again, consistent.
8. Khar-Dushana episode describes a solar eclipse and Hanuman finding Sita accompanied a lunar eclipse; both dates consistent.
9. Now (in 2008) Rama Navami occurs at 21 April, adrift 100 days from 10 Jan. It is consistent with motion of equinox which leads to 1 day adjustment in 72 years, so 100 days in 7200 years.
10. There is literary, geographical, astronomical and local legends around the places mentioned, all supporting Ramayana as history and not mythology. Archaeology is the only thing missing.
11. After 7000 years, easier to find archeological evidence in sea, than land, like Dwaraka was discovered as underwater city.
12. The setu was called Nala setu, later called Rama setu, before muslims and euopians called it Adam Bridge.
13. The construction of the setu is described in great detail. Linear construction. Length 100 yojanas. 1:10 breadth-length ratio. First woods/trees on rock bed, then rocks , etc. Moving aside the accumulated sand, we may get to the wood region, probably carbonated now (can give accurate date).
14. Many kings on both lanka and indian side were called Setupati or similar names. Many coins on kingdoms of both sides have "setu" written on it.
15. Al-Biruni describes the places like Kishkindhya in his book. Marcopolo mentions Ramasetu.
16. Madras presidency manual 1902 mentions that Ramasetu was used as foot bridge till 1480, when a storm destroyed it.
17. NASA satellite images show the possible outline of this underwater bridge
18. Today this waterway is on average 2 meter below water. It should be 1 meter above water originally. Oceanography tells, roughly 9 ft rise in sealevel in 7000 years.