In looking over the laws for keeping food warm over Shabbat, I began to wonder how things practically played out during the times of the Mishna and Talmud. Given that an oven could only be used if the coals were raked out or covered with ash and that only materials which conserved heat and not add to it were allowed, was there ever warm food available on Shabbat day over 12 hours after Shabbat started? I read on Wikipedia (admittedly not always the most reliable source) that chulent only started in the middle ages when baker's ovens were available and people could leave food in it over an extended period of time since the ovens' fires were much more intense and ongoing. Any earlier references would be greatly appreciated.
There were several different methods of leaving food on special stoves and insulating food employed in Talmudic times. One such method was leaving a pot over a special oven-like stove, another involved insulating pots with dry straw or fleece or sesame pulp, as well as wrapping pots in blankets. These methods were largely effective- so effective, in fact, that similar methods were banned as constituting cooking rather than warming or insulating. You can get an in-depth understanding thereof by studying the laws applicable to these practices in Chapter 4 of BT Tractate Shabbat https://www.sefaria.org/Shabbat.47b.8-12?lang=bi