The annual installation, a commemoration of 9/11, shined over Lower Manhattan on Sunday night

Today, as New Yorkers surely know, is the 15th anniversary of the attacks of September 11, 2001, and there have been many tributes around the city today (including the annual reading of the names of those who died, which took place at the World Trade Center site).

One poignant commemoration of the event is the Tribute in Light, which debuted on March 11, 2002, the six-month anniversary of the attacks. The tribute, spearheaded every year by the Municipal Art Society, was initially intended to be a temporary memorial, but it has endured for more than a decade now.

The installation features 88 light bulbs placed into square shapes, so that the beams echo the shape and height of the Twin Towers. And while it’s not without controversy—the beams are responsible for the deaths of hundreds of migratory birds each year, for one—it’s remained one of the most moving tributes to one of the city’s darkest days.

New Yorkers took to social media to share images of the towers of light, both on 9/11 and the day before, when the lights were tested. Check out some of those photos below.

The sadness of this day is palpable and real. It is never far away. One needs only to hear a certain phrase, or to spend a moment listening to the silence, to feel it pierce the heart again. But this day is no longer mostly about sadness and mourning. Fifteen years on, it is now increasingly about the amazingly resilient spirit of New York and New Yorkers, of America and Americans. We are not broken. We have not lost our sense of hope and optimism and belief in the future. We are back, stronger than ever. Just look at this skyline and you know it’s true. So while there is much to mourn on this day, there is also something to celebrate. Have a great day everyone. ✨✌ ️ ✨ ✨ The “Tribute in Light” Sept. 10, 2016. With @gettyphotography @chief770 @clearbluskyes @killahwave @dalton922 @sandyrenee @212sid ✨ ✨ ✨ ✨ ✨ #ny #nyc #nbc4ny #NewYork #newyorkcity #nycdotgram #nycprimeshot #icapture_nyc #picturesofnewyork #what_i_saw_in_nyc #wildnewyork #made_in_ny #ig_nycity #instagramnyc #shotzdelight #arteobjectiva #gotolove_this #createandcapture #thecreatorclass #wanderlust #shotzdelight #igpodium #killeverygram #citykillerz #artofvisuals #theimaged

A photo posted by don doherty (@papakila) on Sep 11, 2016 at 10:51am PDT


A photo posted by Amy (@plitter) on Sep 11, 2016 at 5:31pm PDT

We didn’t ask the taxi to go this way he just did

A photo posted by @michaelstipe on Sep 11, 2016 at 5:41pm PDT

#Neverforget #tributeinlight

A photo posted by Marissa’s Closet (@marissasclosetnyc) on Sep 11, 2016 at 6:19pm PDT

It’s remarkable to think this city has turned something so dark in to something so bright. #neverforget

A photo posted by Patrick (@patrickinthecity) on Sep 11, 2016 at 6:28pm PDT