Yeh, even this is too far a claim to make. Antoninus Pius was not gay like Hadrian clearly was, and already had a natural daughter. His wife was 38 at the time of his ascension, and it was by no means clear that he would a) fail to have a natural son, or b) be unable to produce one in a new marriage. He was clearly still of an age to have children. Yet Hadrian went out of his way to insist on adoption of Aurelius and Verus by Pius, as a condition to becoming emperor, because in his mind at least the best transition plan was to ensure a suitable successor; and he obviously was impressed by the prowess and intellect of the 2 boys. So while Antoninus clearly liked the idea of ensuring his line survived, by marrying his daughter to his own adopted son, it is fairly clear that other considerations were in play than simply aiming for a direct male successor. He could easily have remarried and borne such a child in his 23 year reign. His choice not to suggests a similar line of thinking to Hadrian. This is reconfirmed by the behavior of Aurelius, who waited until after Pius died before he dared name his children (who were literal infants) as his successors. I think a good precedent was established from the time of Augustus that, while it was nice to have your family bloodline passed on and intermixed with the imperial family, a good emperor put a stable succession before that. The undue emphasis on finding a natural male son to succeed is precisely what marred the reign of emperors who sought it out (be it Tiberius, Septimius, or whoever). You can say some of that is post-hoc analysis, yet some of it clearly isn't as I noted above in the Pius situation. Similarly, the very appointment of an adopted son by Augustus (Tiberius), in favour of his blood grandson (Postumus), and you make a similar admission about Britannicus. Aurelius decision was clearly an irresponsible one that ignored much of the precedent set by previous successful emperors. He could have done what Pius himself did; marry his eldest child, his daughter, to a suitable heir (and preserved his bloodline in that way, as Pius did, before it was evident he would or would not have infant sons and Aurelius did).I agree that the issue is a nuanced one. But I think the value of the point originally being made is that some have been inclined to view the Antonine dynasty as a regime that had a preconceived notion that it was better to adopt worthy heirs than to choose a son if available (not that this is what you think; I'm not attempting to strawman you). The reality is that Nerva, Trajan, Hadrian and Antoninus Pius did not have sons. Nerva adopted Trajan to avoid getting overthrown by the Praetorians and the general Nigrinus (based in Syria). Trajan, Hadrian and Antoninus adopted men from within the family rather than biological sons, whom they did not have. This isn't the same thing as what was seen in the Tetrarchic period, when in 293, 305, 308 and 311 biological sons failed to succeed their fathers.