Not the usual stuff!
1. The banks of the Taff once had forts to guard against attacks by the Irish
The Irish were a menacing threat to Roman Britain and forts were built along what is now the Taff to guard against their attacks. Colonies of Irish existed in Wales long after the Romans. Names such as Llyn and Dinllaen are of Irish origin, as was the kingdom of Dyfed, where there are 20 stones inscribed with letters in ogham, from Ireland.
2. Vikings sold the people of Wales as slaves
The Vikings repeatedly attacked Wales in the 10th century. From strongholds in the Isle of Man and Dublin they savaged communities along the coast. It's probably in this time that Scandinavian names, later adopted in English, were given to places like Swansea, Bardsey, Anglesey and Fishguard. There is evidence that the Northmen established small trading stations in Cardiff and there was an extensive stronghold in Anglesey, whose people were sold as slaves. In 987, 2,000 men of the island were captured and sold. The next year, places like Llantwit Major and St Dogmaels were among those plundered.
3. The word 'Sais' was first given to a Welshman who knew how to speak English
'Sais' is still used today in Welsh to describe someone English, sometimes in a derogatory context. However, it was first used in the 15th century to describe a Welshman who knew how to speak English. Welsh people had little reason to know the language in the middle ages, and the use of the word suggests the knowledge was rare and viewed with contempt