Today is the 26th of Tamuz, 5770
The upcoming month of Av is considered a time of mourning, because of the events that took place on this month. Especially the destruction of the first Bet haMikdash (586 BCE) and of the second Bet haMikdash (69 ACE), the Holy Temple of Jerusalem, both of them occurred on the same day, the ninth of Av.
The destruction of our Temple did not consist only on the dismantling of a building. It indeed meant 1. Our exile from the Holy land of Israel, where our connection with God was naturally established. 2. Being now at the mercy of the gentiles and especially, 3. A bitter reminder of 'our transgressions', the reason God Almighty allowed His House to be destroyed.
Even thought we concentrate our mourning on the 9th of Av and a few days before that, our rabbis mentioned a few traditions that should be kept year round to remember that our Temple is still in ruins.
The most known of these customs is that the groom breaks a glass at the end of the wedding ceremony and says: Im eshkakhech Yerushalaim … "If I ever forget you Yerushalaim, may my right hand wither"… If I won't remember Yerushalaim in the happiest moment of my life…
The rabbis also mentioned the custom that the groom places ashes in his head, in the place where he usually wears his Tefillin.
A different angle of the reminders of Jerusalem, the city of David. See http://www.youtube.com/watch?v=AbIlLItLAGs