From their modest beginnings at Treloy before 1216 the family made a series of good marriages, each of which added to their estate, for over two hundred years; by the mid-fifteenth century the estate was almost at its fullest extent, though the later documents printed here show further additions, some by purchase. The first of these marriages was by Ralph, son of Remfrey Arundell, to Eve, a daughter of Richard de Tremodret or Roche, in around 1250—perhaps slightly earlier, since Remfrey II, Ralph's son, was himself married by 1268. Eve brought with her lands in the hundred of Pyder, notably Trembleath (St Ervan), which became the Arundells’ principal residence in the following century; and also some lands further east, in St Minver parish but later attached to the manor of Trembleath. (See below, p. lxv, and the map, p. clv.)

The second marriage came in the next generation, with Remfrey Arundell II, who married the heiress Alice de Lanhern, some time before June 1268. Alice's father John (son of Andrew) de Lanhern was perhaps from a Devonshire family, holding manors of the bishops of Exeter in both counties, though his surname was taken from presumably his preferred residence, in Cornwall. Alice brought with her to the Arundells not only the manor of Lanherne, near to Treloy and Trembleath (and including, at this date, the growing town of St Columb Major: see below, pp. 4-5), but also the Devonshire manors later called Morchard Arundell and Uton Arundell (in the parishes of Morchard Bishop and Crediton), both also held, like Lanherne, of the bishops of Exeter. This was Alice's paternal inheritance; but she brought with her much more than that, for her mother Margery had herself been an heiress, descendant of Richard Pincerna who had received the manor of Connerton, in Penwith, from Robert, son of Robert earl of Gloucester, in about 1155. This was one of the richest manors in west Cornwall, and it was to remain one of the largest in the Arundell estate; it brought with it also the administrative rights of the Hundred of Penwith, the only Cornish hundred to be held in private hands in this way.