Vincent's NT Word Studies
6. Behold (qewreite). See on ch. x. 18.Thrown down. See on Mark xiii. 2.
Robertson's NT Word Studies
21:6 {As for these things} (tauta). Accusative of general reference. {One stone upon another} (liqos epi liqwi). Stone upon stone (locative). Here both #Mr 13:2; Mt 24:2 have epi liqon (accusative). Instead of ouk afeqesetai (future passive) they both have ou me afeqei (double negative with aorist passive subjunctive). It was a shock to the disciples to hear this after the triumphal entry.