וַיְהִ֤י הַשֶּׁ֙מֶשׁ֙ בָּ֔אָה וַעֲלָטָ֖ה הָיָ֑ה וְהִנֵּ֨ה תַנּ֤וּר עָשָׁן֙ וְלַפִּ֣יד אֵ֔שׁ אֲשֶׁ֣ר עָבַ֔ר בֵּ֖ין הַגְּזָרִ֥ים הָאֵֽלֶּה׃
And it came to pass, that, when the sun went down, and there was thick darkness, behold a smoking furnace, and a flaming torch that passed between these pieces.
Read kabbalistic (mystical) interpretation of Genesis 15:17: and classical mystical sources.