In writing, especially about history, ca. is a short way of writing the Latin word circa, which means "about" or "around" when you talk about a date. You put it before a year when nobody is sure of the exact year: ca. 1800 means "sometime around 1800".

In writing在書面裡, especially about history尤其是講歷史的時候, ca. is是 the Latin word circa拉丁字 circa a short way of writing的縮寫, which means意思是 when you talk about a date講日期時的 "about"「大約」 or "around"或「前後」。 when nobody is sure of the exact year沒有人確定是哪一年的時候, You put it你就把它 before a year放在年份前面: ca. 1800 means就是 "sometime around 1800"「大約一八〇〇年前後」。

You will see it on museum labels, in books, and on timelines. It is a writing habit, not a speaking one — people do not usually say "ca" out loud; they say "about" or "around".

You你 on museum labels在博物館說明牌、 in books書裡 and on timelines和年表上 will see it會看到它。 It它 is a writing habit是寫的習慣, not a speaking one不是說的習慣 — people大家 do not usually通常不會 say "ca" out loud把 "ca" 唸出來; they say他們會說 "about" or "around"。

Though actually, some writers use c. with only one letter, and it means the same thing. The little dot is part of the abbreviation, like other short forms in careful writing.

Though actually不過其實, some writers有些作者 use c.只寫 c. with only one letter一個字母, and it means the same thing意思一樣。 The little dot那個小點 is part of the abbreviation是縮寫的一部分, like就像 in careful writing正式書寫裡 other short forms其他縮寫一樣。