As much as Roma, the latest from writer/director Alfonso Cuarón (Gravity, Children of Men, Y Tu Mamá También), is a barely veiled account of his childhood growing up in the middle-class neighborhood of Roma in Mexico City, in truth, it is the story of the two most important women in his life — his mother (renamed Sofia in the film and played by veteran Mexican actress Marina de Tavira) and Cleo (newcomer Yalitza Aparicio), the woman who raised him full time while also taking care of the house and his three siblings (based on a real-life woman named Libo). Easily his most personal and most intimate work to date, Roma finds Cuarón (who also shot and co-edited the film) composing a lyrical, breathtaking look at childhood, as well as the tumultuous times in the city in the early 1970s, which are sometimes only portrayed as background to the more immediate concerns of the family, which was actively being let down and broken apart by careless men.

Mexico’s official selection (and leading contender) for the Best Foreign Language Film Oscar at the 91st Academy Awards, the stunning black-and-white epic is filled with love and chaos, measured melodrama, a spectacular soundscape, and breathtaking performances from both lead actresses, who were cast by Cuarón using a very mysterious process that even they don’t quite understand. And while one of them is a seasoned performer and the other has never acted before, both give performances that are moving and beautifully authentic.

/Film spoke to Aparicio (who spoke through a translator) and De Tavira at the recent Chicago International Film Festival to talk about working with the enigmatic Cuarón and how the realization that they were playing characters deeply important to the filmmaker changed their perception of the overall film. Considered to be one of the finest works of 2018, Roma is in select theaters now, eventually hitting more than 600 theaters worldwide (including 100 in the United States), before it debuts on Netflix on December 14.

I know there was a great deal of secrecy during many phases of Roma’s production, including casting. So how did Alfonso find you both?

Yalitza: It all happened when the casting team came to the community where I lived. There has never, ever been casting in my community before, so my sister insisted that I should go because she wanted to know what casting was all about. And that’s the reason I went. I didn’t want to continue doing the casting process because that would have taken me outside my community, so I had to travel, and I felt scared because for all I knew, this could have been about human trafficking [laughs].

Marina: Well I work as an actress in Mexico, so I’m used to the casting process and auditions, but this one was really different—it was the longest process I’ve done, from the first time in to when I got the part. I think it was about four months or more. The first one I did was also different from all others because there was no scene. They only wanted me to talk about myself, give them a short biography of my life, and then I sensed that they were looking for something that was close to my reality and really going into who I was, and that relaxed me, because there’s no way of getting that wrong.

I’ve heard that you never saw a full script ever during the making of the film. At what point did you realize that your were playing people in his life? Did that terrify or excite you when that was made clear?

Marina: We knew that pretty close to the beginning. We knew that the story came from Alfonso’s memories and that it was about it his family. Yalitza can tell you more because she actually met the real Cleo.

Yalitza: Actually from the very beginning, Alfonso told me that he was going to focus on his mom Libo, and he explained that he actually had two moms: the real one and Libo. After this, he gave me the opportunity to meet Libo, but she only spoke about her story exactly to the point where the movie starts. She didn’t tell me anything that was going to happen in the film, only what had happened before in her life.

Did you both only get the backstory leading up to the events in the movie?

Marina: Exactly. For me it was the same thing, but it was Alfonso who gave me the information. His mother was old and sick, so he told me her story, just to the moment where it starts. Everything that happened before, he told me and the way that Cleo entered their lives, where they had their kids, everything. Then he said, “From now on, you are going to be discovering it day by day.”

Was it entirely improvised? Obviously you knew what was going to happen in each scene, but did you make up what you said?

Marina: There was nothing improvised. It’s hard to explain, because he has a full script, perfectty written, and the film matches it totally. The way he did it was so that it felt improvised. He would give us the lines the same day we shot them, and in very different ways, and always individually. And he would say “You’re going to say something like this. And when she says that, you do this.” Then he would put it all together, and we would see what happened.

Yalitza: Sometimes he gave different instructions to all of us, since he was giving us lines individually. Sometimes I knew what I had to do but then the kids or Marina reacted unexpectedly for me, then I had to react in the moment.

Since you’ve never been in a film before, did you think this just the way movies were made, or did you figure out that this was not normal?

Yalitza: At the beginning, I thought this is how films were made or maybe just a strategy to do it, but I really didn’t know. It was helping because I wasn’t feeling any pressure to study or learn lines or to think or how to show or portray some of the reactions. But when I talked to the crew, they told me that this was absolutely new for them. They had never, ever worked like this and found it really difficult. Then I realized that this was not common, not having a script or anything else to support you ahead of shooting something.

Were you able to shoot this more or less chronologically?

Marina: Totally. And for the producers, it was crazy. They didn’t have the script either and we did it chronologically, so they would arrange for a location and not know whether we were going back to it later.

Both of your characters are in very different circumstances but are abandoned by men, and it becomes a bonding thing between the two of you. Can you talk a bit about that aspect of your characters and how you two lean on each other?

Marina: When Cleo tells Sofia she’s pregnant and that she can’t find the father, it’s the same moment when Sofia has to tell her kids that their father isn’t coming home for Christmas. There’s a moment of silence where Sofia is thinking “We are left alone by men for being mothers.” And that’s what she tells Cleo when she’s a little bit drunk, and I think that’s the situation for a lot of women, and there are lots of women who are heads of families that bring up children by themselves. Somehow it happens in way that the children are of the moms, belong to them, and we really think we have the strength when the father isn’t a presence in their lives.

Yalitza: This is a very tough but real situation that many women face. The abandonment, like in the case of Sofia, her children area abandoned when they are still little, while Cleo, she’s still pregnant when she is abandoned. Men just leave. As Marina said, Sofia tells Cleo, “No matter what they tell you, we are always alone.” When we were shooting the scene, I remember it made me cry because I started thinking that no matter what society says or what your friends tell you, these women have to move on, struggle and do whatever it takes to solve the problems of their families and overcome any situation. And if the men leave, it’s even more so. They have to get together, stick together and overcome everything to bring their families up and out of it.