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Historical sources and dating: BC and AD — History, 11–13

What a historical source is, how material remains speak about the past and how to place events in time.

Sources, and a timeline to place them

A historical source is any trace of the past that gives us information about it. It can be material — tools, pottery, buildings, coins —, written — letters, laws, inscriptions —, oral — stories that are told — or visual, like paintings and photographs. To place events in time we use the calendar that counts years from the birth of Christ: before Christ (BC) and after Christ (AD).

Why History needs evidence

We cannot travel to the past to see what happened. So historians and archaeologists work like detectives: they look for traces, dig, compare and draw conclusions. Without sources, a story is only an opinion. And without reliable dates, we cannot tell what came before what, or what caused what.

A case: questioning a fragment of pottery

Step 1: at a castro, an archaeologist finds a fragment of pottery — a material source. Step 2: she asks what it tells us: people stored or cooked food, and the decoration shows the taste and skill of whoever made it. Step 3: she notes the soil layer it lay in, next to Roman coins: so it probably dates from Roman times. Step 4: she notices what it does not say — names, language, ideas — and looks for other sources.

The trap: reading the dates backwards

With BC dates the numbers count backwards: 500 BC is older than 200 BC, because it is further from year 1. And there is no year zero: after 1 BC comes AD 1. So if one event is from 200 BC and another from AD 300, the gap is about 500 years, not 100. Centuries work the same way: the 1st century starts in year 1, and the 21st century starts in 2001.

Where you can still see this today

Every museum in Portugal shows historical sources: pottery, coins, tools and inscriptions. At Conímbriga, near Coimbra, you can see a Roman city with mosaics and houses uncovered by archaeologists. And your own home has sources too: photographs, letters and family objects tell the story of those who lived before you.

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