Rama.As the date of birth of Poigai Azhwar is 4025 BC,these temples should have existed before 4025 BC
Now if you want to visit Nalanda,the Railway station where you have to alight is Bakhtiyarpuramed after the man who destroyed Nalanda
This type of worship is called Saguna Upasna, Worship of Reality with Attributes.
Lord Krishna explains to Arjuna that He(Krishna) appears and grants the wishes of His Devotees in the Name and Form He is addressed
At those who have attempted had lost their eyesight.
The information is credible as it comes from a descendant of Thirupathi Archakas who have been serving Him since 19th Century.
There is a temple near Kumbakonam,Tamil Nadu for relief from poisonous bites and life threatening fever.