Why is my setInterval for a carousel not working?

let diapositiveActuelle = 1;

afficherDiapositives(diapositiveActuelle);

function diapositiveSuivante(n) {
  afficherDiapositives(diapositiveActuelle += n);
}

function afficherDiapositives(n) {
  let i;
  let diapositives = document.getElementsByClassName("Galerie");

  if (n > diapositives.length) {
    diapositiveActuelle = 1;
  }
  if (n < 1) {
    diapositiveActuelle = diapositives.length;
  }

  for (i = 0; i < diapositives.length; i++) {
    diapositives[i].style.display = "none";
  }

  diapositives[diapositiveActuelle - 1].style.display = "block";
}

setInterval(function() {
  diapositiveActuelle++;
  afficherDiapositives(diapositiveActuelle);
}, 3000);

.Galerie {
  display: none
}

img {
  vertical-align: middle;
}

.Carousel {
  max-width: 70%;
  position: relative;
  margin: auto;
  transition: scale 1000ms;
  cursor: zoom-in;
}

.Carousel :hover {
  scale: 110%;
}

.avant,
.suivant {
  cursor: pointer;
  position: absolute;
  top: 60%;
  width: auto;
  padding: 16px;
  margin-top: -10vh;
  color: white;
  font-size: 3vh;
}

.suivant {
  right: 0;
  border-radius: 3px 0 0 3px;
}

<div class="Carousel">

  <div class="Galerie " style="display: block;">

    <img src="/Images/Slider/1.jpeg" style="width:100%">
  </div>

  <div class="Galerie ">
    <img src="/Images/Slider/2.jpeg" style="width:100%">
  </div>

  <div class="Galerie ">
    <img src="/Images/Slider/3.jpeg" style="width:100%">
  </div>

  <div class="Galerie ">
    <img src="/Images/Slider/4.jpeg" style="width:100%">
  </div>

  <div class="Galerie ">
    <img src="/Images/Slider/5.jpeg" style="width:100%">
  </div>

  <div class="Galerie ">
    <img src="/Images/Slider/6.jpeg" style="width:100%">
  </div>

  <a class="avant" onclick="diapositiveSuivante(-1)">&#10094</a>
  <a class="suivant" onclick="diapositiveSuivante(1)">&#10095</a>

</div>