The longer-standing language of Wales is Welsh, belonging to the Celtic branch of the Indo-European family. The first major incursions of English came in the wake of the Norman invasion of Wales, which began towards the end of the eleventh century AD. Dialects of Welsh English influenced by the south-west of England existed from the twelfth century onwards. Under the Acts of Union of 1536-1543, English was made the sole language of government and law in Wales. Higher prestige and increasing incoming speaker numbers helped establish English as a language of the whole of Wales by the second half of the twentieth century. Regional dialects in particular have had the greatest influence overall on the special character of English in Wales. There are notable differences between the traditional Welsh dialects of north and south Wales. Thus it is possible to talk of two main types of Welsh English, one centred in the north-west, the other in the mid-south. In these main northern and southern sub-varieties, non-standard features tend to be derived from Welsh-language influence. But there are other determining factors, such as influence from the neighbouring non-standard dialects (rural and urban) of England, particularly but not exclusively in the border areas, south Pembrokeshire and Gower.