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|Ab urbe condita||862|
|Balinese saka calendar||30–31|
|Chinese calendar||戊申年 (Earth Monkey)|
2805 or 2745
— to —
己酉年 (Earth Rooster)
2806 or 2746
|Coptic calendar||−175 – −174|
|- Vikram Samvat||165–166|
|- Shaka Samvat||30–31|
|- Kali Yuga||3209–3210|
|Iranian calendar||513 BP – 512 BP|
|Islamic calendar||529 BH – 528 BH|
|Minguo calendar||1803 before ROC|
|Seleucid era||420/421 AG|
|Thai solar calendar||651–652|
235 or −146 or −918
— to —
236 or −145 or −917
Year 109 (CIX) was a common year starting on Monday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Palma and Tullus (or, less frequently, year 862 Ab urbe condita). The denomination 109 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
- June 24 – The Aqua Traiana is inaugurated by Emperor Trajan; the aqueduct channels water from Lake Bracciano, 40 kilometers (25 mi) north-west of Rome.
- The Via Traiana is constructed at the Emperor Trajan's personal expense; the road connects Benevento with Brundisium (Brindisi).
- The Baths of Trajan, built by the architect Apollodorus of Damascus, are dedicated during the Calends.[when?] The thermae are constructed on the platform of the Palace of Nero (Domus Aurea) in Rome.
- Osroes I of Parthia succeeds his brother Pacorus II, and rules over the western Parthian Empire.
- Pliny the Younger is legate to Bithynia.