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Archaeologists try to discover as much as they can about the past. They are not the same as historians who use written records. Archaeologists look for things; things made by people, used by people, or even the remains of the people themselves.
GridsWhen archaeologists are investigating a site, they carefully mark it out with a grid and slowly dig down removing the soil carefully so that they don't disturb anything that is buried in it. When they find something they gently remove the soil from around it until it is free to be lifted away. They record where they found it (by drawing a diagram or taking a photograph showing where it was in relation to the grid) and then examine the object itself. Many objects need to be carefully cleaned before they can be fully identified. Some are broken and the pieces need to be painstakingly fitted together. Often only one or two pieces of an object are found and the archaeologists must work out what the rest was like based on things they've seen before.
The sorts of things that archaeologists find and study ranges from enormous buildings (like the Colosseum in Rome or the Theatre here in Lepcis) to small buildings (like the house in Lepcis that this web site will tell you about) to personal objects (like the glass bottle found in that house) small objects (like the ear-ring found in the house) and even tiny things (such as seeds and grape pits).

As well as studying the objects themselves, archaeologists want to know when the objects were made or used or put in the ground. They try to work this out using a technique called stratigraphy.
StrataIf an object is buried in the ground (either deliberately or by accident) and some time later another object is buried too, the second object will, usually, be above the first object. So if you are digging to find objects you will find newer objects before older objects. Of course sometimes people dig holes into the ground and newer objects finish up lower, and that's what makes it so difficult for the archaeologists!
For example, in this picture of a cross-section through a site, the Phoenician remains (at the deepest levels in the middle of the picture) are obviously older than the Roman remains of walls and a hypocaust above them; but the foundations for the column in the middle have been dug into the Phoenician remains. So the archaeologists compare the type of wall and the way it was built with the other Roman buildings and Phoenician buildings to decide if it belongs with the older Phoenician remains or is an intrusion from the later Roman period (or indeed if it was originally Phoenician and re-used/rebuilt by the Romans).
If a number of different objects are found at the same level, with no evidence of intrusion from later levels, then they are likely to date from the same time. If some of them are known to come from a particular date (either because the style is the same as something found elsewhere with a known date, or because it is itself dated like a coin, or because it can be chemically analysed to estimate its age) then all of them can be treated as coming from that date too.
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