Bhaktas while traveling from Keezh (lower) Tirupathi to Tirumala (Mel Tirupathi), we have to travel 7 hills only after traveling these hills, we can reach the Tirumala, where the Kali Yugha Deivam, Thiruvenkadamudayaan is giving his seva to Bhaktas. The following details explain about the 7 Malais (mountains).
Virushabahtri:
This is the first hill we will be crossing. This mountain is also called as "Erunndhumalai". Once, there lived an arakkan (demon) by named "Virushasooran", who gave lots of trouble to the people, but he was a great Narasimha bhaktan. Because of this, he had got a varam (boon) that his death should come only by the Emperumaan. But even though he was a great Narasimha bhaktan, he was giving trouble to the people and finally the Perumal through his Vishnu Chakkaram killed him and as requested by him at the time of his death, this mountain is named as "Virushabathri" (or) "Virushasalam".
Neelathri:
After crossing the first hill, Virushabathri, we will be traveling to the second hill, which is called as "Neelathri". It is also called as "Neelamalai". This name is given to this hill to remember the blue colour of Sri Vishnu. (Sri Vishnu has another Thirunaamam as "Neela megha Shyamalan")
Anjanathri:
This is the third hill, we will be traveling to get the seva of Sri Balaji. This hill is named as "Anjanathri", since Anjana devi, mother of Lord Hanuman, did a strong tapas and as a result of this only, the hill is named as such. This mountain is also called as "Anjanasalam".
Seshathri:
The fourth hill is Seshathri hill, which is next to Anjanathri hill. It is believed that Aadhiseshan is turned as the series of hills and withstanding the Nindra Kola Thiruvenkadamudayan. To explain the greatness of Aadhiseshan, this fourth hill is named as "Seshathri" (or) "Seshaasalam".
Garudathri:
It is believed that the Perumal came to this sthalam on Garudan and to explain this, this 5th hill is named as "Garudathri" (or) "Garudaasalam".
Narayanathri:
This is the sixth mountain found while traveling to Tirumala. This hill is named so that it explains the 6 characters (Om Na ra ya na ya) of Sriman Narayanan.
Thiruvenkadam:
This is the final mountain and this is also called as "Eazhu Malai". Bhaktas will be very happy to cross this 7th hills, since after crossing this, they will be getting the seva of Thiruvenkadamudayan, who is said to extract all kinds of sorrows of human life. This 7th hill is also named as "Venkadathri".
This hill is said to have the character of curing diseases and is said to contain medicinal values.
Once, there lived an andhanan, by named Purandharan. He had a bad character and led his life by enjoying with women and as a result of this, he got some sort of incurable diseases. And after being left out by the women, he came to this Tirumala and finally he was cured completely. His body was badly affected and is termed to be "Kadam". And after he reached this mountain, his Kadam, the sin was turned to Punyam (Opposite to sin) and his body turned as pure as gold (Which becomes pure after being treated with fire). Because of this, this Tirumala is also called as "Venkadam". Eazhumala, Tirumalai, Vadamalai are the other names of Thiruvenkadam.