Wearing a black skullcap, he paused in front of the holiest site where Jews can pray, then placed what appeared to be a written prayer or note between its stones, as is custom.
Trump was not accompanied by any Israeli leaders during the hugely symbolic visit.
Allowing them to do so could have led to accusations that Washington was implicitly recognizing Israel's unilateral claim of sovereignty over the site, which would break with years of US and international precedent.
Security was tight, with the usually bustling Old City, where the Western Wall is located, essentially on lockdown and the plaza leading to the site cleared.
As Trump's convoy of dozens of cars entered the square around 4:00 pm (1300 GMT), armed security forces were positioned on nearly every building nearby as well as on the outer wall of the Old City.
In the nearby Jewish Quarter, barriers had been erected to make viewing the square impossible from ground level, and some residents said they had been told not to go onto their roofs overlooking the Western Wall.
Simon, a 20-year-old American studying in a nearby Jewish seminary, said he was "excited" by Trump's visit but disappointed he would not see him.
Around a dozen ultra-Orthodox Jewish men had crammed into a tiny terrace on top of one house looking over, seemingly having been granted permission.
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