[誤] There used to be a palace here before long.
[正] There used to be a palace here long before.
注:不要想當然地以為 before long 是指“在很久以前”,恰恰相反,它的意思是“不久以后”,例如:Harry Porter will be published before long(《哈利. 波特》不久就要出版了)。而 long before 才相當于 long,long ago,表示“在很久很久以前”。