diff --git a/src/layers/shipwrecks/records.js b/src/layers/shipwrecks/records.js
index c1d17e77b..741adb320 100644
--- a/src/layers/shipwrecks/records.js
+++ b/src/layers/shipwrecks/records.js
@@ -194,18 +194,43 @@ function wikiUrl(value) {
 
 /**
  * A Wikidata time as a day ("1912-04-15") when it is day-precise, else as a
- * year only: a month- or year-precise value reads back as the 1st.
- * @returns {{date: string|null, year: number|null}}
+ * year only: a month- or year-precise value reads back as the 1st. A year
+ * before AD 100 ("-0299", 300 BC) has no place on the year picker, so it is
+ * kept as ancient with its year as text, like EMODnet's period-dated wrecks.
+ * @returns {{date: string|null, year: number|null, dating: string|null}}
  */
 function wikidataTime(value, precision) {
-  const match = /^(-?\d{4})-(\d{2})-(\d{2})T/.exec(value || '');
-  if (!match) return { date: null, year: null };
-  const year = parseYear(match[1]);
-  const p = Number(precision);
-  // 11 = day; 9 = year; 10 = month. A missing precision (P576) counts as a day.
-  if (!Number.isFinite(p) || p >= 11)
-    return { date: `${match[1]}-${match[2]}-${match[3]}`, year };
-  return { date: null, year: p >= 9 ? year : null };
+  const none = { date: null, year: null, dating: null };
+  const match = /^([+-]?)(\d{4,})-(\d{2})-(\d{2})T/.exec(value || '');
+  if (!match) return none;
+  // A missing precision (P576 is read without one) counts as a day.
+  const p = precision == null ? 11 : Number(precision);
+  // 11 = day; 10 = month; 9 = year; below 9 is a decade or coarser.
+  if (!Number.isFinite(p) || p < 9) return none;
+  const signed = Number(`${match[1] === '-' ? '-' : ''}${match[2]}`);
+  if (signed < 100) {
+    // The query service writes XSD 1.1 years: 0000 is 1 BC, -0299 is 300 BC.
+    const dating = signed <= 0 ? `${1 - signed} BC` : `AD ${signed}`;
+    return { date: null, year: null, dating };
+  }
+  const year = parseYear(String(signed));
+  if (year === null) return none;
+  if (p >= 11)
+    return { date: `${match[2]}-${match[3]}-${match[4]}`, year, dating: null };
+  return { date: null, year, dating: null };
+}
+
+/** Whether a record (or a parsed time) says when the ship sank. */
+function hasWhen(when) {
+  return Boolean(when.date || Number.isInteger(when.year) || when.dating);
+}
+
+/** Copy when a ship sank from one record (or parsed time) to another. */
+function takeWhen(target, from) {
+  target.date = from.date ?? null;
+  target.year = from.year ?? null;
+  target.dating = from.dating ?? null;
+  target.ancient = Boolean(from.dating) || Boolean(from.ancient);
 }
 
 /** "sinking of the RMS Titanic" → "Sinking of the RMS Titanic". */
@@ -233,10 +258,7 @@ export function normalizeWikidataResults(payload) {
     if (known) {
       // Extra rows only add what the first one lacked.
       known.vesselType ||= clean(value('typeLabel'), 60);
-      if (!known.date && !known.year) {
-        known.date = sunk.date || ended.date;
-        known.year = sunk.year ?? ended.year;
-      }
+      if (!hasWhen(known)) takeWhen(known, hasWhen(sunk) ? sunk : ended);
       known.casualties ??= count(value('deaths'));
       known.survivors ??= count(value('survivors'));
       continue;
@@ -249,7 +271,7 @@ export function normalizeWikidataResults(payload) {
     if (!validPoint(lat, lon)) continue;
     const name = clean(value('itemLabel'), 100);
     const event = value('event') === 'event';
-    const when = sunk.date || sunk.year ? sunk : ended;
+    const when = hasWhen(sunk) ? sunk : ended;
     byItem.set(qid, {
       id: `wikidata:${qid}`,
       source: 'wikidata',
@@ -261,8 +283,8 @@ export function normalizeWikidataResults(payload) {
       vesselType: event ? null : clean(value('typeLabel'), 60),
       year: when.year,
       date: when.date,
-      dating: null,
-      ancient: false,
+      dating: when.dating,
+      ancient: Boolean(when.dating),
       cause: null,
       notes: impersonalText(value('itemDescription'), MAX_TEXT),
       cargo: null,
@@ -313,10 +335,7 @@ function foldSinkingEvents(records) {
       continue;
     }
     twin.vesselType ||= record.vesselType;
-    if (!twin.date && !twin.year) {
-      twin.date = record.date;
-      twin.year = record.year;
-    }
+    if (!hasWhen(twin)) takeWhen(twin, record);
     twin.casualties ??= record.casualties;
     twin.survivors ??= record.survivors;
   }
@@ -335,9 +354,8 @@ function foldSinkingEvents(records) {
       out.push(event);
       continue;
     }
-    if (!ship.date && !ship.year) {
-      ship.date = event.date;
-      ship.year = event.year;
+    if (!hasWhen(ship)) {
+      takeWhen(ship, event);
     } else if (!ship.date && event.date && event.year === ship.year) {
       ship.date = event.date;
     }
@@ -395,7 +413,7 @@ export function mergeShipwreckRecords(emodnet = [], wikidata = []) {
       kept.push(record);
       continue;
     }
-    twin.year ??= record.year;
+    if (!hasWhen(twin)) takeWhen(twin, record);
     twin.vesselType ||= record.vesselType;
     twin.cause ||= record.cause;
     twin.depth ??= record.depth;
diff --git a/src/layers/shipwrecks/records.test.mjs b/src/layers/shipwrecks/records.test.mjs
index e65863331..61ec8fe64 100644
--- a/src/layers/shipwrecks/records.test.mjs
+++ b/src/layers/shipwrecks/records.test.mjs
@@ -222,3 +222,43 @@ test('a sinking event folds into its ship; month-precise dates keep the year onl
   assert.equal(concordia.date, '2012-01-13');
   assert.equal('event' in concordia, false);
 });
+
+test('a date before AD 100 is kept as ancient text, never read as an AD year', () => {
+  const entity = (q) => ({ value: `http://www.wikidata.org/entity/${q}` });
+  const [bc, earlyAd, roman] = normalizeWikidataResults({
+    results: {
+      bindings: [
+        {
+          item: entity('Q1'),
+          itemLabel: { value: 'Antikythera wreck' },
+          coord: { value: 'Point(23.3 35.9)' },
+          sunk: { value: '-0299-01-01T00:00:00Z' },
+          sunkPrecision: { value: '11' },
+        },
+        {
+          item: entity('Q2'),
+          itemLabel: { value: 'Early wreck' },
+          coord: { value: 'Point(12 40)' },
+          sunk: { value: '0050-01-01T00:00:00Z' },
+          sunkPrecision: { value: '9' },
+        },
+        {
+          item: entity('Q3'),
+          itemLabel: { value: 'Roman wreck' },
+          coord: { value: 'Point(13 41)' },
+          sunk: { value: '0300-01-01T00:00:00Z' },
+          sunkPrecision: { value: '9' },
+        },
+      ],
+    },
+  });
+  assert.equal(bc.year, null, '300 BC is not the year 300');
+  assert.equal(bc.date, null, 'no day for a BC date');
+  assert.equal(bc.dating, '300 BC');
+  assert.equal(bc.ancient, true);
+  assert.equal(earlyAd.year, null);
+  assert.equal(earlyAd.dating, 'AD 50');
+  assert.equal(earlyAd.ancient, true);
+  assert.equal(roman.year, 300);
+  assert.equal(roman.dating, null);
+});