To get some sense of how Easter was calculated after Dionysius by people who lacked computers (or even Arabic numerals), I here transcribe an actual table from a manuscript written in 1004. I will reproduce it as exactly as I can, including abbreviations.

In one of these periodic reexaminations of the issue, the problem was handed over to one Dionysius Exiguus (Denis the Little, or as I like to call him, Denis the Scrawny). Dionysius reported back reaffirming the Alexandrian method of calculation, and since the tables currently in use were about to expire, he also took the opportunity to calculate the dates of Easter for the next 532 years. The tables he produced and the introductory letter have survived. To the beginning of his tables he prefaced the last 19 years of the old tables. Those tables identified the year in the year of Diocletian (sometimes called the Era of the Martyrs, for the great persecutions of Christians that took place under that emperor), years 228-247 to be precise. When Dionysius continues his table, however, he dates the years in the cycle from the incarnation of Christ (anno domini is Latin for "year of the lord"), as he believed them to be. In his letter, he explains that he preferred that Jesus, not a persecutor of Christians, be remembered in his tables. The first year in his continuation is 532, which is thus equated with the year of Diolcetian 248. To provide another correlation to a known count of years, Dionysius also indicates the year of the indiction, a 15-year cycle used in the late Roman empire for purposes of taxation. AD 532 was the 10th year of the indiction, according to Dionysius.

In 325 CE, the Council of Nicaea met. One of its primary tasks was to ensure a uniformity of observation in liturgical matters, particularly with respect to the observation of Easter. The council decreed that Easter should be kept on the same day everywhere, and from the evidence of a surviving letter, it seems that the Alexandrian church was to make the standard calculations. Just because the Alexandrian church was tasked with calculating Easter does not mean they continued to rely upon astronomers to supply them with the actual date of the vernal equinox.

From at least the 2^nd century CE, there was prolonged controversy over what date upon which the passion of Jesus ought to be celebrated. Much of the confusion stems from ambiguity in the biblical account. All four gospels clearly state that Jesus rose from the grave on the first day of the week (now called Sunday), three days after the crucifixion. They also, however, refer to the Last Supper with relation to Passover, which begins on Nisan 15 (see the Jewish calendar). The synoptic gospels imply it was a Passover meal, but John says it was on the day before Passover (Nisan 14).

In his Ecclesiastical History of the English, the eighth-century historian Bede repeatedly mentions the controversy between the Irish and the Roman churches over the correct calculation of Easter. As Bede sees it, the culminating moment in this battle comes at the synod of Whitby when both sides present their arguments before king Oswy, who decided in favor of the Roman method. From our distance, the argument may seem rather silly—an argument over how many angels can dance on the head of a pin.

The Julian calendar was a major improvement over the older Roman calendar. The rule for leap years was simple enough that anyone could keep track of it, and the calendar stayed pretty much in time with the solar year. But just how accurate was the Julian calendar?

The Romans took the start of the year to be January 1, just as we do. In examining other documents, however, particularly medieval ones, we need to be aware that such was not always the case. In the Byzantine empire, September 1 was the beginning of the new year. In the West, January 1 persisted, but alongside of that you also find year the beginning on December 25, March 25, or even Easter. Most of the early Western reluctance to use January 1 as the year's beginning stemmed from Christian disapproval of the traditional pagan ceremonies held on January 1.

The Julian calendar was a modification by Julius Caesar of the Republican calendar. As pontifex maximus, Caesar was responsible for the smooth operation of Rome's calendar, which previous neglect had allowed to fall behind the seasons. In the second year of Caesar's dictatorship (707 AUC = 47 BCE) the calendar was running seriously behind the solar year. Some scholars have argued it was 90 days behind, and Caesar began by ordering an ordinary (pre-Julian) leap year (with the extra month).