The Antonidas Memorial is located between the Magus Commerce Exchange and Sunreaver's Sanctuary in Dalaran. It is a monument to the late archmage Antonidas, the previous leader of the Kirin Tor, who was killed by Arthas Menethil shortly before the fall of Dalaran.
Tides of War
After Theramore fell, Jaina visited the memorial, and had an argument with Kalecgos when he refused her to aid her in destroying the Horde.
Purge of Dalaran
This section concerns content exclusive to Mists of Pandaria.
Before the Storm
Following the Argus Campaign, Kalecgos and Jaina met here again. She confirmed that she would not be returning and had to continue finding her own place.
A marker stone was added when Wrath of the Lich King went live which reads:
Archmage Antonidas, Grand Magus of the Kirin Tor
The great city of Dalaran stands once again - a testament to the tenacity and will of its greatest son.
Your sacrifices will not have been in vain, dearest friend.
With Love and Honor,
While not stated, Antonidas could be have been transported after rebuilding Dalaran and made this monument his final resting place.