There's long been concern that the conflict in Syria could spill over into neighboring countries.
Turkey and Lebanon have seen some of that spill-over.
And now… so has Israel.
Monday, Syrian mortar shells landed in the Israeli-occupied Golan Heights.
The Israeli army says it fired back and scored "direct hits" on the Syrian artillery units involved.
Syria and Israel have technically been at war for decades but that the border between the two countries has been quiet.
But, this is the first time since 1973 that the Syrians and Israelis have shot at each other across the ceasefire line.
Despite an Egyptian brokered ceasefire agreement, Israeli officials say the shells were mistakenly fired and drifted in Israeli territory. But, Israeli Prime Minister Benjamin Netanyahu is taking it seriously.
Netanyahu is under pressure to do what it takes to keep Israel safe and he is said to be contemplating a a stringer military operation.