# Time subdivisions

There may be a span of dates, e.g. AA5-7, but no more than three centuries. If the book covers a greater period than that, prefer not to use a time subdivision. Also do not leave an open span of dates, e.g. AA9-.

<table data-header-hidden><thead><tr><th width="124.5873015873016">Column1.1</th><th width="619">Column1.2</th></tr></thead><tbody><tr><td><strong>.AA0</strong></td><td>Prehistoric (-3500 BC)<br><mark style="background-color:red;">Prehistoric means before the dawn of the great civilisations of the Near and Far East, ca. 3500 BC (technically before the invention of writing). Civilisation did not arise till later in Europe and the Americas, so the title and content should dictate the cataloguer’s choice of term.</mark></td></tr><tr><td><strong>.AA1</strong></td><td>Ancient period (3500BC-500 AD)</td></tr><tr><td><strong>.AA2</strong></td><td>Middle Ages (500-1300)</td></tr><tr><td><strong>.AA3</strong></td><td>14th century</td></tr><tr><td><strong>.AA4</strong></td><td>15th century</td></tr><tr><td><strong>.AA5</strong></td><td>16th century</td></tr><tr><td><strong>.AA6</strong></td><td>17th century</td></tr><tr><td><strong>.AA7</strong></td><td>18th century</td></tr><tr><td><strong>.AA8</strong></td><td>19th century</td></tr><tr><td><strong>.AA9</strong></td><td>20th century</td></tr><tr><td><strong>.AA10</strong></td><td>21st century</td></tr></tbody></table>