そのころ
そのころ · sonokoro · JLPT N2 · noun
days
⌛ そのころ = その (that) + ころ (about the time) = that about-the-time, i.e. back then
ころ means a rough point in time, like around-the-time. その points back to a time already mentioned, so the whole word means that time, then.