diff --git a/docs/reference/search.md b/docs/reference/search.md
index b7af8138..daa9c0e7 100644
--- a/docs/reference/search.md
+++ b/docs/reference/search.md
@@ -289,6 +289,20 @@ directly.
 | `date`               | `range` (inclusive)  | yes   | yes              | ISO 8601 string (surface)                                                             |
 | `boolean`            | `is`                 | yes   | –                | boolean (absent = false)                                                              |
 
+A **`date`** is stored as Unix seconds – a sortable, range-filterable integer –
+and is ISO 8601 at every edge: the projection converts a value on the way in,
+the query compiler converts a filter bound on the way out, and the surface emits
+a string. A year outside the plain four-digit form is accepted however it is written –
+expanded (`-001100-01-01T00:00:00.000Z`) or not (`-1100`, `-250000`, `25000`):
+the codec pads it to the signed six digits `Date` needs before parsing, so the
+same value indexes and filters alike. Deep time is real data – SCHEMA-AP-NDE
+blesses years beyond four digits for `schema:dateCreated` – and an unpadded year
+would otherwise parse as something else entirely (a BCE year as a UTC offset,
+landing in the wrong era; a five-digit CE year as a legacy local-time date,
+landing a year early and differently per host timezone), without ever failing.
+The window is the one `Date` can represent, ±271,821 years around 1970; a year
+outside it leaves the field absent, as any unparseable value does.
+
 **`array` decides a field’s shape**, whatever the graph carries: a declared
 `array` field stores a list, and a single-valued one stores the first value –
 for every kind alike, so the projection, the engine collection definition
diff --git a/packages/search-typesense/test/query-compiler.test.ts b/packages/search-typesense/test/query-compiler.test.ts
index 22f5512f..d8d7951c 100644
--- a/packages/search-typesense/test/query-compiler.test.ts
+++ b/packages/search-typesense/test/query-compiler.test.ts
@@ -413,6 +413,30 @@ describe('buildSearchParams', () => {
     ).toBe(`datePosted:<=${max}`);
   });
 
+  it('reads an unpadded BCE bound as a year, so the range is not inverted', () => {
+    const min = Date.parse('-001100-01-01T00:00:00.000Z') / 1000;
+    const max = Date.parse('-000800-01-01T00:00:00.000Z') / 1000;
+    expect(
+      buildSearchParams(
+        {
+          ...base,
+          where: [
+            {
+              or: [
+                {
+                  field: 'datePosted',
+                  range: { min: '-1100', max: '-0800' },
+                },
+              ],
+            },
+          ],
+        },
+        schema,
+      ).filter_by,
+    ).toBe(`datePosted:[${min}..${max}]`);
+    expect(min).toBeLessThan(max);
+  });
+
   it('compiles orderBy: RELEVANCE → _text_match and a localized field → its sort key', () => {
     expect(
       buildSearchParams(
diff --git a/packages/search/src/project.ts b/packages/search/src/project.ts
index d17f1dd1..75a95716 100644
--- a/packages/search/src/project.ts
+++ b/packages/search/src/project.ts
@@ -230,11 +230,17 @@ function applyField(
         ? derivedIris(derived)
         : // A derived `date` goes through the same storage codec as a read one:
           // the field is stored as Unix seconds, so an ISO string returned here
-          // would otherwise land as a string in an int64 field. A derive that
-          // already computed seconds returns a number and passes through.
+          // would otherwise land as a string in an int64 field.
           field.kind === 'date' && typeof derived === 'string'
           ? isoToUnixSeconds(derived)
-          : derived;
+          : // A derive that computed seconds itself returns a number, which the
+            // codec never saw and so never range-checked. Seconds outside what
+            // `Date` can represent – reachable now that deep time is – would
+            // store fine and then throw on every read at the surface, where an
+            // unparseable string merely leaves the field absent. Drop it too.
+            field.kind === 'date' && typeof derived === 'number'
+            ? storableSeconds(derived)
+            : derived;
     // NaN is not a value any kind stores, and a derive is the only route that
     // can produce one (`setNumber` guards the read route). It serializes as
     // `null`, which an engine rejects for a numeric field – so drop it, leaving
@@ -588,6 +594,13 @@ function derivedIris(value: unknown): unknown {
   return typeof value === 'string' && isAbsoluteIri(value) ? value : undefined;
 }
 
+/** Stored Unix seconds a `Date` can represent, or `undefined` – the same
+ *  answer {@link isoToUnixSeconds} gives a string it cannot parse, so the two
+ *  routes into a `date` field agree on what is storable. */
+function storableSeconds(seconds: number): number | undefined {
+  return Number.isNaN(new Date(seconds * 1000).getTime()) ? undefined : seconds;
+}
+
 function toInteger(literal: string | undefined): number | undefined {
   return literal === undefined ? undefined : Math.trunc(Number(literal));
 }
diff --git a/packages/search/src/schema.ts b/packages/search/src/schema.ts
index eb431a18..bdfa755b 100644
--- a/packages/search/src/schema.ts
+++ b/packages/search/src/schema.ts
@@ -1454,10 +1454,38 @@ const ABSOLUTE_IRI = /^[A-Za-z][A-Za-z0-9+.-]*:\S*$/;
  * unparseable value.
  */
 export function isoToUnixSeconds(iso: string): number | undefined {
-  const millis = new Date(iso).getTime();
+  // Trim first: XSD collapses whitespace around a date literal before parsing,
+  // so a padded lexical form is legal and reaches here verbatim. Left in place
+  // it defeats the year expansion below in both directions – a leading space
+  // stops the match, a trailing one survives it into the legacy parser – and
+  // each lands the value in a different year than it reads.
+  const millis = new Date(expandYear(iso.trim())).getTime();
   return Number.isNaN(millis) ? undefined : Math.trunc(millis / 1000);
 }
 
+/**
+ * Pad a year outside the plain four-digit form to the signed six digits ISO
+ * 8601 expects, so `Date` reads it as a year at all. Deep time is real data,
+ * not a corner case: SCHEMA-AP-NDE blesses years beyond four digits for
+ * `schema:dateCreated`. Left unexpanded, neither era parses as written and
+ * neither fails loudly – `-1100` is read as a bare UTC offset and lands
+ * around 1100 **CE** (shifted by the host’s offset), `25000` is read as a
+ * legacy local-time date and lands a year early, on a boundary that moves
+ * with the host’s timezone. Either way nothing throws, no field is left
+ * absent, and the value sorts and filters as if it were another date
+ * entirely. A plain four-digit year and an already-expanded one pass through
+ * unchanged, so the form the API itself emits round-trips.
+ */
+function expandYear(iso: string): string {
+  // The year, then the rest: a non-digit stops the run, so a longer digit
+  // string (epoch millis, say) is left alone rather than cut into a year.
+  const year = /^([+-]?)(\d{1,6})(\D.*|)$/.exec(iso);
+  if (year === null || (year[1] === '' && year[2].length === 4)) {
+    return iso;
+  }
+  return `${year[1] || '+'}${year[2].padStart(6, '0')}${year[3]}`;
+}
+
 /** The inverse of {@link isoToUnixSeconds}: stored Unix seconds → ISO 8601. */
 export function unixSecondsToIso(seconds: number): string {
   return new Date(seconds * 1000).toISOString();
diff --git a/packages/search/test/project.test.ts b/packages/search/test/project.test.ts
index 444e1173..ff347185 100644
--- a/packages/search/test/project.test.ts
+++ b/packages/search/test/project.test.ts
@@ -557,6 +557,14 @@ describe('projectDocument', () => {
             kind: 'date',
             derive: () => Date.parse('not-a-date') / 1000,
           },
+          // Seconds past what `Date` can represent are dropped too: stored,
+          // they read back as an error at the surface rather than as a value,
+          // where an unparseable string simply leaves the field absent.
+          {
+            name: 'temporal',
+            kind: 'date',
+            derive: () => -8_640_000_000_001,
+          },
         ],
       },
     );
@@ -564,6 +572,7 @@ describe('projectDocument', () => {
     expect(document.modified).toBe(1_704_067_200);
     expect(document).not.toHaveProperty('created');
     expect(document).not.toHaveProperty('available');
+    expect(document).not.toHaveProperty('temporal');
   });
 
   it('holds a reference to absolute IRIs on every route a value can arrive by', () => {
diff --git a/packages/search/test/schema.test.ts b/packages/search/test/schema.test.ts
index b26f7165..67166e7e 100644
--- a/packages/search/test/schema.test.ts
+++ b/packages/search/test/schema.test.ts
@@ -1445,4 +1445,68 @@ describe('date storage codec', () => {
   it('returns undefined for an unparseable date', () => {
     expect(isoToUnixSeconds('not-a-date')).toBeUndefined();
   });
+
+  it('reads an unpadded BCE year as a year, not as a UTC offset', () => {
+    const seconds = isoToUnixSeconds('-1100');
+    expect(unixSecondsToIso(seconds ?? 0)).toBe('-001100-01-01T00:00:00.000Z');
+    expect(seconds).toBe(isoToUnixSeconds('-001100-01-01T00:00:00.000Z'));
+  });
+
+  it('reads a CE year beyond four digits, independent of the host timezone', () => {
+    expect(unixSecondsToIso(isoToUnixSeconds('25000') ?? 0)).toBe(
+      '+025000-01-01T00:00:00.000Z',
+    );
+    expect(unixSecondsToIso(isoToUnixSeconds('25000-06-01') ?? 0)).toBe(
+      '+025000-06-01T00:00:00.000Z',
+    );
+  });
+
+  it('leaves a plain four-digit year and an expanded one alone', () => {
+    expect(unixSecondsToIso(isoToUnixSeconds('1999') ?? 0)).toBe(
+      '1999-01-01T00:00:00.000Z',
+    );
+    expect(
+      unixSecondsToIso(isoToUnixSeconds('+025000-01-01T00:00:00.000Z') ?? 0),
+    ).toBe('+025000-01-01T00:00:00.000Z');
+  });
+
+  it('reads a deep-time BCE year beyond four digits', () => {
+    expect(unixSecondsToIso(isoToUnixSeconds('-250000') ?? 0)).toBe(
+      '-250000-01-01T00:00:00.000Z',
+    );
+    expect(unixSecondsToIso(isoToUnixSeconds('-38000') ?? 0)).toBe(
+      '-038000-01-01T00:00:00.000Z',
+    );
+  });
+
+  it('expands the year of a fuller BCE date, leaving the rest alone', () => {
+    expect(unixSecondsToIso(isoToUnixSeconds('-1100-05-03') ?? 0)).toBe(
+      '-001100-05-03T00:00:00.000Z',
+    );
+  });
+
+  it('reads a whitespace-padded year as the year it spells', () => {
+    // XSD collapses whitespace around a date literal, so a padded form is legal
+    // and reaches the codec verbatim.
+    for (const padded of [' -1100', '\t-1100', '-1100 ', '  -1100  ']) {
+      expect(isoToUnixSeconds(padded)).toBe(isoToUnixSeconds('-1100'));
+    }
+    expect(isoToUnixSeconds(' 25000 ')).toBe(isoToUnixSeconds('25000'));
+    expect(isoToUnixSeconds('  1999  ')).toBe(isoToUnixSeconds('1999'));
+  });
+
+  it('returns undefined for a year beyond what Date can represent', () => {
+    // ±271,821 years is the edge of the Date range; past it there is no value
+    // to store, so the field is left absent as an unparseable string is.
+    expect(isoToUnixSeconds('-500000')).toBeUndefined();
+    expect(isoToUnixSeconds('-271821')).toBeUndefined();
+  });
+
+  it('orders BCE before CE, and earlier BCE before later', () => {
+    const deepTime = isoToUnixSeconds('-250000') ?? 0;
+    const bce = isoToUnixSeconds('-1100') ?? 0;
+    const ce = isoToUnixSeconds('1100') ?? 0;
+    expect(deepTime).toBeLessThan(bce);
+    expect(bce).toBeLessThan(ce);
+  });
 });
diff --git a/packages/search/vite.config.ts b/packages/search/vite.config.ts
index 661f9376..e3f60542 100644
--- a/packages/search/vite.config.ts
+++ b/packages/search/vite.config.ts
@@ -12,7 +12,7 @@ export default mergeConfig(
         thresholds: {
           functions: 100,
           lines: 100,
-          branches: 99.56,
+          branches: 99.57,
           statements: 100,
         },
       },