diff --git a/web/e2e/helpers.ts b/web/e2e/helpers.ts
index ebf61fd..3d881a4 100644
--- a/web/e2e/helpers.ts
+++ b/web/e2e/helpers.ts
@@ -1,4 +1,4 @@
-import type { Browser, Page } from '@playwright/test';
+import { expect, type Browser, type Page } from '@playwright/test';
 
 export const DOC = '/g/monnaie-libre/docs/acte-engagement-certification';
 export const TEST_DOC = '/g/essai/docs/acte-engagement-certification';
@@ -138,3 +138,74 @@ export async function chain(page: Page, docPath = DOC) {
       (await page.request.post(`${base}/control/${what}`)).json(),
   };
 }
+
+/**
+ * The welcome (Yvv, 2026-11-02), in French: the keystone arch shelters the three points, the
+ * toolbox first, each centred under the keystone in the opening; then the title, centred, on
+ * two lines broken after « possible ». Nothing tilted, nothing past the edges of the screen.
+ * Measured once the arch has settled (its entrance done).
+ */
+export async function expectWelcome(page: Page) {
+  await expect(page.locator('.vault .leitmotiv li')).toHaveText(['boîte à outils', 'contexte et cadrage', 'processus et modalités']);
+  const h1 = page.getByRole('heading', { level: 1 });
+  await expect(h1).toHaveText('Rendre possible la décision collective');
+  await expect(h1.locator('.line')).toHaveText(['Rendre possible', 'la décision collective']);
+  const m = await page.evaluate(async () => {
+    const intro = document.querySelector('.intro')!;
+    await Promise.all(intro.getAnimations({ subtree: true }).map((a) => a.finished));
+    const text = (el: Element) => {
+      const r = document.createRange();
+      r.selectNodeContents(el);
+      return { box: r.getBoundingClientRect(), rects: r.getClientRects().length };
+    };
+    const v = document.querySelector('.vault')!.getBoundingClientRect();
+    // The arch in its own units: 92 wide (x from −46), the top of the keystone at y = −40.
+    const u = v.width / 92;
+    const at = (x: number, y: number) => ({ x: v.left + (x + 46) * u, y: v.top + (y + 40) * u });
+    const points = [...document.querySelectorAll('.leitmotiv li')].map((li) => {
+      const { box, rects } = text(li);
+      // Back into the arch's units, from its axis and its springing line (y = 0).
+      return { rects, left: (box.left - at(0, 0).x) / u, right: (box.right - at(0, 0).x) / u, top: (box.top - at(0, 0).y) / u, bottom: (box.bottom - at(0, 0).y) / u };
+    });
+    const h = document.querySelector('h1')!.getBoundingClientRect();
+    const lines = [...document.querySelectorAll('h1 .line')].map((l) => ({ ...text(l), block: l.getBoundingClientRect() }));
+    const tilted = [document.querySelector('.vault svg')!, ...document.querySelectorAll('.vault svg path')]
+      .flatMap((n) => {
+        const out: string[] = [];
+        for (let e: Element | null = n; e && e !== document.body; e = e.parentElement) {
+          const cs = getComputedStyle(e);
+          const flat = cs.transform === 'none' || /^matrix\(1, 0, 0, 1, /.test(cs.transform);
+          if (!flat || (cs.rotate && cs.rotate !== 'none')) out.push(`${e.tagName} ${cs.transform} ${cs.rotate}`);
+        }
+        return out;
+      });
+    return {
+      overflow: document.documentElement.scrollWidth - innerWidth,
+      axis: v.left + v.width / 2,
+      vaultBottom: v.bottom,
+      points,
+      title: { top: h.top, axis: h.left + h.width / 2 },
+      lines: lines.map(({ box, rects, block }) => ({ rects, top: block.top, bottom: block.bottom, axis: box.left + box.width / 2 })),
+      tilted,
+    };
+  });
+  expect(m.overflow, 'nothing past the edge of the screen').toBeLessThanOrEqual(0);
+  expect(m.tilted, 'the arch is never tilted').toEqual([]);
+  // The three points: one line each, top to bottom, centred on the axis, under the keystone (its
+  // foot at y = −19), between the imposts (x = ±19) and above the slab (y = 15.6); a line that
+  // rises above the springing line stays clear of the voussoirs, closer in there (x = ±17).
+  for (const [i, p] of m.points.entries()) {
+    expect(p.rects, `point ${i}: one line`).toBe(1);
+    expect(Math.abs((p.left + p.right) / 2), `point ${i}: centred`).toBeLessThan(0.3);
+    expect(p.top, `point ${i}: under the keystone`).toBeGreaterThan(-19);
+    expect(p.bottom, `point ${i}: above the slab`).toBeLessThan(15.6);
+    expect(p.right, `point ${i}: in the opening`).toBeLessThan(p.top < 0 ? 17 : 19);
+    if (i > 0) expect(p.top, `point ${i}: under the one before`).toBeGreaterThan(m.points[i - 1]!.top);
+  }
+  // The title: under the arch, centred on its axis, two lines of one line each.
+  expect(m.title.top).toBeGreaterThanOrEqual(m.vaultBottom);
+  expect(Math.abs(m.title.axis - m.axis)).toBeLessThan(1);
+  expect(m.lines.map((l) => l.rects)).toEqual([1, 1]);
+  expect(m.lines[1]!.top).toBeGreaterThanOrEqual(m.lines[0]!.bottom - 1);
+  for (const l of m.lines) expect(Math.abs(l.axis - m.axis)).toBeLessThan(1);
+}
diff --git a/web/e2e/mobile.spec.ts b/web/e2e/mobile.spec.ts
index 15ffc4f..6357a22 100644
--- a/web/e2e/mobile.spec.ts
+++ b/web/e2e/mobile.spec.ts
@@ -1,5 +1,5 @@
 import { expect, test, type Locator } from '@playwright/test';
-import { DOC, shot, signIn } from './helpers';
+import { DOC, expectWelcome, shot, signIn } from './helpers';
 
 /** WCAG contrast ratio of two CSS colours `rgb(r, g, b)`. */
 function contrast(a: string, b: string): number {
@@ -25,13 +25,19 @@ async function backdrop(el: Locator): Promise<string> {
   });
 }
 
-test('M1 — mobile : logo dans la barre, menu en tiroir, vote déplié, panier, réglages lisibles, pastilles au clavier', async ({ page }) => {
+test('M1 — mobile : logo dans la barre, l’accueil sous la voûte, menu en tiroir, vote déplié, panier, réglages lisibles, pastilles au clavier', async ({ page }) => {
   await signIn(page, 'Chiara');
   await page.goto('/');
   const brand = page.locator('header.topbar a.brand');
   await expect(brand).toHaveAccessibleName('libreDecision');
   await expect(brand.locator('svg')).toBeVisible();
   await expect(page.locator('a.root')).toContainText('Monnaie libre');
+  // The welcome on this phone, then on a narrow one (360): the arch still shelters the three points.
+  await expectWelcome(page);
+  const size = page.viewportSize();
+  await page.setViewportSize({ width: 360, height: 780 });
+  await expectWelcome(page);
+  if (size) await page.setViewportSize(size);
   await page.goto(DOC);
   await page.getByRole('button', { name: 'Menu' }).click();
   const drawer = page.getByRole('dialog', { name: 'Boîte à outils' });
diff --git a/web/e2e/reader.spec.ts b/web/e2e/reader.spec.ts
index 009571b..e4766c3 100644
--- a/web/e2e/reader.spec.ts
+++ b/web/e2e/reader.spec.ts
@@ -1,10 +1,9 @@
 import { expect, test } from '@playwright/test';
-import { BOB, DOC, person, signIn, TEST_DOC, wallet } from './helpers';
+import { BOB, DOC, expectWelcome, person, signIn, TEST_DOC, wallet } from './helpers';
 
-test('C1 — l’accueil sans session : le titre, le leitmotiv en trois lignes, la connexion, le menu complet', async ({ page }) => {
+test('C1 — l’accueil sans session : la voûte abrite les trois points, le titre centré en deux lignes, la connexion, le menu complet', async ({ page }) => {
   await page.goto('/');
-  await expect(page.getByRole('heading', { level: 1 })).toHaveText('Rendre possible la décision collective');
-  await expect(page.locator('.leitmotiv li')).toHaveText(['contexte et cadrage', 'processus et modalités', 'boîte à outils']);
+  await expectWelcome(page);
   const nav = page.getByRole('navigation', { name: 'Boîte à outils' });
   for (const item of ['Décisions', 'Docs de référence', 'Mandats', 'Protocoles']) {
     await expect(nav.locator('.tool', { hasText: item })).toBeVisible();
diff --git a/web/src/lib/i18n/en.ts b/web/src/lib/i18n/en.ts
index 53f7543..50e861e 100644
--- a/web/src/lib/i18n/en.ts
+++ b/web/src/lib/i18n/en.ts
@@ -30,7 +30,8 @@ export const en: Messages = {
   'nav.menu': 'Menu',
   'nav.close': 'Close',
 
-  'home.title': 'Making collective decisions possible',
+  'home.title.line1': 'Making it possible',
+  'home.title.line2': 'to decide together',
   'home.leitmotiv.context': 'context and framing',
   'home.leitmotiv.process': 'processes and methods',
   'home.leitmotiv.tools': 'a toolbox',
diff --git a/web/src/lib/i18n/es.ts b/web/src/lib/i18n/es.ts
index b5a606f..144df45 100644
--- a/web/src/lib/i18n/es.ts
+++ b/web/src/lib/i18n/es.ts
@@ -30,7 +30,8 @@ export const es: Messages = {
   'nav.menu': 'Menú',
   'nav.close': 'Cerrar',
 
-  'home.title': 'Hacer posible la decisión colectiva',
+  'home.title.line1': 'Hacer posible',
+  'home.title.line2': 'la decisión colectiva',
   'home.leitmotiv.context': 'contexto y encuadre',
   'home.leitmotiv.process': 'procesos y modalidades',
   'home.leitmotiv.tools': 'caja de herramientas',
diff --git a/web/src/lib/i18n/fr.ts b/web/src/lib/i18n/fr.ts
index ed9159e..2a922d3 100644
--- a/web/src/lib/i18n/fr.ts
+++ b/web/src/lib/i18n/fr.ts
@@ -33,7 +33,9 @@ export const fr = {
   'nav.menu': 'Menu',
   'nav.close': 'Fermer',
 
-  'home.title': 'Rendre possible la décision collective',
+  // The title on two lines, the break after « possible » (Yvv, 2026-11-02): one key per line.
+  'home.title.line1': 'Rendre possible',
+  'home.title.line2': 'la décision collective',
   'home.leitmotiv.context': 'contexte et cadrage',
   'home.leitmotiv.process': 'processus et modalités',
   'home.leitmotiv.tools': 'boîte à outils',
diff --git a/web/src/routes/+page.svelte b/web/src/routes/+page.svelte
index f25707b..26d6b08 100644
--- a/web/src/routes/+page.svelte
+++ b/web/src/routes/+page.svelte
@@ -1,17 +1,28 @@
 <script lang="ts">
+  // The welcome (Yvv, 2026-11-02): the keystone arch, large enough to shelter the three points of
+  // the leitmotiv, the toolbox first; then the title, centred, broken after « possible ».
+  import sign from '$lib/assets/cle-de-voute.svg?raw';
   import GroupChoice from '$lib/components/GroupChoice.svelte';
   import { t } from '$lib/i18n/index.svelte';
   import { session } from '$lib/session.svelte';
+
+  const LEITMOTIV = ['home.leitmotiv.tools', 'home.leitmotiv.context', 'home.leitmotiv.process'] as const;
 </script>
 
 <div class="home">
   <header class="intro">
-    <h1>{t('home.title')}</h1>
-    <ul class="leitmotiv">
-      <li>{t('home.leitmotiv.context')}</li>
-      <li>{t('home.leitmotiv.process')}</li>
-      <li>{t('home.leitmotiv.tools')}</li>
-    </ul>
+    <div class="vault">
+      <span class="sign" aria-hidden="true">{@html sign}</span>
+      <ul class="leitmotiv">
+        {#each LEITMOTIV as key, i (key)}
+          <li style:--i={i}>{t(key)}</li>
+        {/each}
+      </ul>
+    </div>
+    <h1>
+      <span class="line">{t('home.title.line1')}</span>
+      <span class="line">{t('home.title.line2')}</span>
+    </h1>
   </header>
 
   {#if session.me}
@@ -28,56 +39,127 @@
   .home {
     max-width: 44rem;
     margin: 0 auto;
-    padding: clamp(3rem, 10vh, 6.5rem) clamp(1.2rem, 5vw, 3.5rem) 5rem;
+    padding: clamp(2rem, 7vh, 4.5rem) clamp(1.2rem, 5vw, 3.5rem) 5rem;
     display: grid;
     gap: clamp(2.4rem, 6vh, 3.6rem);
   }
-  .intro h1 {
-    font-family: var(--font-text);
-    font-weight: 500;
-    font-size: clamp(2.1rem, 1.4rem + 3vw, 3.4rem);
-    letter-spacing: -0.015em;
-    line-height: 1.08;
-    font-variation-settings: 'opsz' 72;
-    max-width: 15ch;
-    text-wrap: balance;
+
+  /* The arch, drawn by the sign of the logo (stones in the ink of the mood, the keystone in
+     `--cle`), never tilted. Its box is the stone itself: 92 units wide (the base slab, x from
+     −46 to 46) and 59 high (y from −40, the top of the keystone, to 19, under the slab); the SVG's
+     own 3-unit margin spills out above and below (clipped on the sides, where it is empty). On a
+     phone the arch reaches into the side padding, 0.75rem short of the screen's edges, so that the
+     opening keeps as much room as it can. */
+  .vault {
+    --w: min(34rem, 100vw - 1.5rem);
+    container-type: inline-size;
+    position: relative;
+    width: var(--w);
+    margin-inline: calc(50% - var(--w) / 2);
+    aspect-ratio: 92 / 59;
+    overflow-x: clip;
+    color: var(--ink);
   }
-  /* The leitmotiv: three lines, each set on a small stone of the keystone's colour. */
+  .sign {
+    position: absolute;
+    inset: calc(-300% / 59) calc(-300% / 92);
+  }
+  .sign :global(svg) {
+    display: block;
+    width: 100%;
+    height: 100%;
+  }
+  /* The light under the vault: the opening (x from −18.5 to 18.5, from the keystone down to the
+     slab), its top a half circle, washed with the keystone's colour. */
+  .vault::before {
+    content: '';
+    position: absolute;
+    inset: calc(2150% / 59) calc(2750% / 92) calc(340% / 59);
+    border-radius: 50% 50% 0 0 / 54.25% 54.25% 0 0;
+    background: radial-gradient(
+      ellipse 75% 62% at 50% 60%,
+      color-mix(in srgb, var(--cle) 12%, transparent),
+      transparent
+    );
+  }
+
+  /* The three points, sheltered: centred in the opening (x from −19 to 19; a band from y = −19,
+     under the keystone, to 19, centred on the springing line y = 0), one line each. The type
+     follows the arch (cqi): the longest line of the three languages, 10.5 em (es), holds in the
+     38 units of the opening with room to spare. On a phone the italic is small (12px at 360):
+     its advances are kept exact, not rounded to the pixel, or the letters drift apart
+     (« pr ocessus ») and the word spaces close up. */
   .leitmotiv {
-    list-style: none;
-    margin: 1.4rem 0 0;
+    position: absolute;
+    inset: calc(2100% / 59) calc(2700% / 92) 0;
+    margin: 0;
     padding: 0;
+    list-style: none;
     display: grid;
-    gap: 0.2rem;
+    align-content: center;
+    justify-items: center;
+    gap: 0.2em;
     font-family: var(--font-text);
     font-style: italic;
-    font-size: clamp(1.12rem, 1rem + 0.55vw, 1.4rem);
-    line-height: 1.45;
+    font-size: 3.55cqi;
+    line-height: 1.3;
     color: var(--ink-soft);
+    white-space: nowrap;
+    text-align: center;
+    text-rendering: geometricPrecision;
   }
-  .leitmotiv li {
-    display: flex;
-    align-items: baseline;
-    gap: 0.7rem;
+
+  .intro h1 {
+    margin-top: clamp(1.4rem, 4vh, 2.4rem);
+    font-family: var(--font-text);
+    font-weight: 500;
+    font-size: min(3.3rem, 8.6vw);
+    letter-spacing: -0.015em;
+    line-height: 1.1;
+    font-variation-settings: 'opsz' 72;
+    text-align: center;
   }
-  .leitmotiv li::before {
-    content: '';
-    flex: none;
-    width: 0.62em;
-    height: 0.34em;
-    border-radius: 0.1em;
-    background: var(--cle);
-    opacity: 0.75;
-    translate: 0 -0.12em;
+  .line {
+    display: block;
+    text-wrap: balance;
   }
+
   .enter {
-    display: flex;
-    flex-wrap: wrap;
-    align-items: center;
-    gap: 0.6rem 1.2rem;
+    display: grid;
+    justify-items: center;
+    gap: 0.8rem;
+    text-align: center;
+  }
+  .enter .btn {
+    min-height: 2.75rem;
+    padding-inline: 1.4rem;
   }
   .enter p {
     font-size: 0.9rem;
     max-width: 34ch;
   }
+
+  /* The keystone sets the arch, then the three points come under it. */
+  @media (prefers-reduced-motion: no-preference) {
+    .sign :global(path[fill^='var(--cle']) {
+      transform-box: fill-box;
+      animation: settle 0.7s var(--ease) 0.1s backwards;
+    }
+    .leitmotiv li {
+      animation: appear 0.6s var(--ease) backwards;
+      animation-delay: calc(0.55s + var(--i) * 0.12s);
+    }
+  }
+  @keyframes settle {
+    from {
+      transform: translateY(-40%);
+      opacity: 0;
+    }
+  }
+  @keyframes appear {
+    from {
+      transform: translateY(0.4em);
+      opacity: 0;
+    }
+  }
 </style>