# Time periods

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MARC Field: `648`

1st indicator: \[blank]

2nd indicator: `4`

`(we`use second indicator `4` rather than using 2nd indicator `7` in combination with `|2`local)
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Only add a time period heading, if the item is *about* a specific time period, i.e. COVID-19 Pandemic: Defining the 21st century.
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Since October 2006, we have used 648 for entering stand-alone expressions of time coverage.

This is part of the library’s policy of splitting up subject strings, and is done in preference to using `650` `|y`

648 is not covered by AACP.

Terms used locally in 648 are:

&#x20;Prehistoric

Ancient

Medieval (note spelling)

xxth century (note punctuation and choice of case)

For definitions of Prehistoric, Ancient and Medieval, see list below, which matches the list of Barnard time subdivisions.

## TIME PERIOD HEADINGS

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Copy & paste genres into a new field in Sierra. They will format automatically with correct field tag
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`d648 4`**Prehistoric (-3500 BC)**

`d648 4`**Ancient (3500 BC-500 AD)**

`d648 4`**Medieval (500-1300)**

`d648 4`**14th century.**

`d648 4`**15th century.**

`d648 4`**16th century.**

`d648 4`**17th century.**

`d648 4`**18th century.**

`d648 4`**19th century.**

`d648 4`**20th century.**

`d648 4`**21st century.**

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.

Ancient and Medieval are not exclusive terms; i.e. 10th century is a valid heading.

`648` is technically repeatable, but normal practice is to use hyphenated forms, e.g.

`d648 4`**15th-17th centuries.**

`d648 4`**12th-14th centuries.**

`d648 4`**Medieval-16th century.**

Hyphenated spans are never left open; i.e. **do not use** 18th century-

(use e.g. 18th-21st centuries)

General Collections usage of `648` (and Barnard time subdivisions) generally confines spans to no more than three centuries. This is not prescriptive.

Remember: a `650_0` for a specific event may also be added to a record, eg

`650 0` **World War, 1939-1940.**

Note that the LCSH heading

`650_0`**Medicine**`|x`**History**`|y`**To 1500.**

is used for **all** periods up to 1500.
