Sun arrives at Aries - Songkran

That all people were under the same umbrella, is clear from the fact that, we all share the same sense of year, month and week, since ancient times.

The Gregorian calendar based on  Roman calendar, is similar to our present day Indian almanac - the Panchanga.

The Indian lunar year begins in the new moon of March - Ugadi.

Initially, the Roman calendar also marked the new year in March.
And they named the seventh month as September -Saptha-, the eighth as Ashta or October, the ninth as Nawa or November and the tenth as Dasha or December.

As a contrapposto, in India, there is evidence of January being marked as the first month of a year. Month of Mrgasirsha, or mid- December to mid-January, is referred to as Agrahayanam. 

We can infer that in each land, people reckoned a month, as the transit of Sun in a zodiac sign.

- Shri Chandrashekarendra Saraswati, Kanchi