The doorway and windows are made possible by placing over the open spaces thick stone beams that support the weight from above.(中文：可在空地用石條搭建門(mén)窗,石條可以承受門(mén)窗上面的重量.）
1.這句話是被動(dòng)語(yǔ)態(tài).
2.句子后半部分placing over open spaces thick stone beams 從語(yǔ)法上講可改寫(xiě)為placing thick stone beams over open spaces.比如：put+名詞+over=put+over+名詞,但若這里的名詞是代詞如：it 的話,語(yǔ)法規(guī)定則只能發(fā)在中間,即put it over.
3.而原文那樣的語(yǔ)序,也是有道理的.因?yàn)樵摼浜竺嬗幸粋€(gè)定語(yǔ)從句（that support the weight from above),因此為了避免先行詞混淆,故把thick stone beams 放在over后面,以便緊跟從句,避免混淆.
僅供參考!