'The Romans' is a huge thing. The legendary date for the foundation of the Roman Empire was 753bc, although of course they went back much further than that in reality. Until 27bc was the time of the Roman Republic (where Rome was ruled by the Senate), but after that Rome was ruled by the Emperors until the barbarian invasions destroyed the empire in ad476. Mostly, when people think of 'the Roman Empire', they think of the heyday of the Emperors from Augustus (27bc) to Commodus (died ad192).
The Anglo-Saxons traditionally started their invasions with Hengist and Horsa who according to the Anglo-Saxon Chronicle were invited to Britain in ad449. After ad793 (Viking raid on Lindisfarne) the A-Ss overlap the Vikings, but the Anglo-Saxon era came to an end in 1066.
'The Normans' strictly only refers to William I, William II, Henry I, Stephen and Matilda (1066-1154). After that (Henry II onwards, they were the 'Plantagenets').
The 'Middle Ages' refers to the period between the end of the Roman Empire (ad476) and the beginning of the 'Renaissance' (which was traditionally dated as starting with Columbus's discovery of America in ad1492). This included a period people call the 'Dark Ages', stretching from, ad476 to about ad1000, and a period generally called the 'High Middle Ages', which stretched from 1066 to 1492. Again, when people talk about 'the Middle Ages', they are generally talking about the 'High Middle Ages'.
I have to tell you that every historian puts different dates on all these periods - there is no generally agreed 'right' or 'wrong' about the dates. the dates I have given you are more-or-less 'it'-ish.
As to centuries. The first hundred years after the death of Christ (the first 'century') started in the year 1 and ended with the year 100. Thus the second century was the years 101-200. The third century was 201-300 etc. until the 21st century, which is the years 2001 to 2100.
NOTE that the newspapers got it wrong. They all celebrated the millennium and the end of the 20th century at midnight on 31 December 1999. WRONG!!!! The year 2000, of course, was properly in the 20th century, and people should have celebrated the millennium at midnight on 31 Decembe 2000 (and indeed there was a small number of very sad historians who did so).
Anyway, as you are a pupil, you are desperate for me to SHUT UP!!! and tell you 'the answer', so, focussing on what are popularly accepted as the 'heyday' of each of your eras:
Roman Empire - 1st century BC to 2nd century AD.
Anglo-Saxons - 5th to 11th centuries AD.
Normans - 11th to 12th centuries AD.
Middle Ages - 11th to 15th centuries AD.
Does this make sense.
If you can understand all the fiddly-faffing about the details, you will impress the hell out of your teacher, who is just LONGING for someone to actually give a damn about these things!
