וַיַּ֤עַשׂ לַמִּזְבֵּ֙חַ֙ מִכְבָּ֔ר מַעֲשֵׂ֖ה רֶ֣שֶׁת נְחֹ֑שֶׁת תַּ֧חַת כַּרְכֻּבּ֛וֹ מִלְּמַ֖טָּה עַד־חֶצְיֽוֹ׃
And he made for the altar a grating of network of brass, under the ledge round it beneath, reaching halfway up.
Read kabbalistic (mystical) interpretation of Exodus 38:4: and classical mystical sources.