The tenth of Tevet is the first in a series of events which ended in the destruction of the first Beit Hamikdash.
As a reminder of the destruction a chatan breaks a glass under the chupa uttering
the words of:
אם אשכחך ירושלים תשכח ימיני
תדבק לשוני לחכי אם לא אזכרני
אם לא אעלה את ירושלים על ראש שמחתי
In our homes we leave a section of a wall by the entrance unpainted reminding us that there is no complete joy as long as the Beit Hamikdash is not yet rebuilt.
Using Paintings, Mosaic Tiles, Wording, Glass, Stones or Art people are very creative in commemorating the destruction of the Beit Hamikdash in their homes.
Pictured above, is in my brother Amram's home. They adhered to the halachic guidelines of keeping an "ama by an ama" of unpainted wall and they beautified the area around the unfinished square.
Along the top, appear King David's words from Tehillim:
.על נהרות בבל, שם ישבנו גם בכינו, בזכרנו את ציון. על ערבים בתוכה תלינו כנרותינו
"By the Rivers of Babylon, there we sat and also wept when we remembered Zion" - A clear prophecy to the time when the Jews were escorted to Babylon and sat by the water after days of walking. There, in the Diaspora, by the rivers of Babylon, they sat, wept and reflected on Jerusalem and their Holy Temple. The famous phrase of אם אשכחך ירושלים תשכח ימיני frames the two sides and bottom of the unfinished square.
We look forward to the day when our complete joy is returned to us with the rebuilding of the Third and Eternal Beit Hamikdash.