Which is really interesting and i think only is said with her nightblade skin. However i cant find any contextual lore around this and it would be really cool if someone could give insights on what the placidium was. and what was important about it that would be cool!
Since others gave you the lore, I'll just drop a tiny bit of info - she says it on all her skins, or should anyway.
"The Placidium of Navori
Situated at the heart of the continent, the Placidium is one of Ionia’s most sacred places. Many have journeyed here to study at renowned schools, or meditate in its wild, magical gardens. Undoubtedly, this was why it became such a tempting target for the invading armies of Noxus..."
https://universe.leagueoflegends.com/en_US/region/ionia/?mv=image-gallery
"The Great Stand
It was at the Placidium that the people of Ionia finally took up arms against their Noxian enemies. But the cost of that day’s victory was immense, and some now question if fighting back was the right decision, since the harmonious balance of their homeland may have been lost forever."
She cut off Swains arm there, no?
