To upgrade your Altar, you need Ceremonial Stones.
With each upgrade, you need more Ceremonial Stones.
Below is a list of possible ways to gain these.
Gems
You can purchase Ceremonial Stones using gems.
1 Ceremonial Stone = 15 Gems
10 Ceremonial Stones = 125 Gems
100 Ceremonial Stones = 1,154 Gems
1000 Ceremonial Stones = 10,000 Gems
Campaign Elite Sweeps
You can sweet elite campaigns to pick up extra Ceremonial Stones.
Elite 8-1
Elite 8-2
Elite 8-3
Elite 8-4
Elite 8-5
Elite 8-6
Chests
Chest from the VIP daily clan gifts (Nightspear city) gives Ceremonial Stones too.
VIP Daily Clan Gifts
You can collect 5 Ceremonial Stones per gift from daily VIP Clan gifts (Once you have level 25 diplomacy for this city).