Christian wrote: “..when we speak about Buddha’s meditation we always speak about Three marks, 8-fold Path, Paticca Samupadda etc.’
Yes. You can do that while in all four postures.
– In addition to contemplating on those (and even before being able to do that), one must get into the habit of being mindful of one’s actions. See the post referred below.
In Buddhist temples, there are walking paths. In some old temples, there are designated “walking paths” between two statues of a Buddha facing the walkway.
We need to remember that Anapanasati and Satipatthana meditations are supposed to be done at all times, especially to determine if one’s action is wise or not.
– See, “Kāyānupassanā – Section on Postures (Iriyāpathapabba)”
P.S. By the way, Ven. Ananda attained the Arahanthood while in none of the above four postures. He was contemplating a Dhamma concept while getting ready to go to bed. The phala moment came when he was in the process of lying down. He was not standing but had not got to the lying down position on the bed.
– So, he was contemplating that concept, and the “clarification” came in that particular instant where his feet were off the ground, but he had not yet fully landed on the bed!
– If anyone remembers the sutta, please post. If I come across it, I will post it here.