Alltwen lies on the south eastern banks of the river Tawe, opposite the larger Pontardawe, and its southern boundaries are defined by Nant Llechau, which flows westwards past the village before joining the Tawe. The first edition of the 25inch OS maps, published in 1877, shows that employment for residents of Alltwen came from the flour mill and chemical works on its western boundaries. There was also a railway station and a public house on the northern edge of Alltwen, near Pont Ar Dawe bridge (NPRN 43138). Alltwen was centred around its two public houses - the Butcher's Arms and The Rock - and it's Independent chapel (NPRN 10063) whilst the houses primarily extended from the centre to the north, the south east and the south west along three roads.
The second edition of the 25inch OS maps, published in 1898, labels these roads as 'Gwyn Street' (heading from south west from the centre of Alltwen) and Alltwen Road, which begins north of the village at the Pont Ar Dawe bridge and associated public house before heading south east through Alltwen. The village did not appear to have experienced much change between 1877 and 1898. It had lost its flour mill but gained a church dedicated to St. John the Baptist (NPRN 13403) two unnamed public houses, a post office, and a Sunday School associated with the Independent chapel in addition to an Infant school and some terraced workers houses nearer the northern edge of the village.
By the time the fourth edition of the 25inch OS maps was published in 1942, there had been substantial residential development in Alltwen and it now expanded some half a mile to the north west, another half a mile to the south west and quarter of a mile to the south east from its original centre. Another primary school and post office had been built, along with a children's playground and a Congregational chapel, all in the northern half of the village.
In the twenty-first century, Alltwen's northern boundaries are defined by an industrial estate. The original infants school has closed but the school that appeared near Pont ar Dawe on the fourth edition of the 25inch OS maps remains open and educates approximately 230 pupils aged three to eleven. Other amenities in the village include a convenience store, a rugby club, St. John the Baptist's church, the Independent chapel and the Butchers public house and The New Lodge.
Sources: modern and historic OS maps; google maps; Estyn report on Alltwen Primary School published in October 2018
M. Ryder, RCAHMW, 22nd February 2019