This cavalry regiment (ala) was formed in Gaul and named after its first commander Sebosiana. This cavalry unit of 500 men was in Carlisle in the year 105 (see https://www.jstor.org/stable/30030577) and a tombstone was found at Inveresk in Musselburgh around 140 AD (see https://archaeology.co.uk/articles/bodyguards-corpses-and-cults.htm and https://canmore.org.uk/site/295681/carberry). They trained with lances, bows, slings and javelins. It was at Lancaster probably after 125 AD, with a standard compliment. An inscription shows that this regiment was back for a period in the middle third century.