Latin ), with Bulgarian copies dating from the 13th century, and Serbian versions from the 14th century. Medieval Christian traditions associated with the lucky or unlucky nature of certain days of the week survived into the modern period. This concerns primarily Friday, associated with the crucifixion of Jesus. Sunday, sometimes personified as Saint Anastasia, was itself an object of worship in Russia, a practice denounced in a sermon extant in copies going back to the 14th century. Sunday, in the ecclesiastical numbering system also counted as the or the first day of the week; yet, at the same time, figures as the "eighth day", and has occasionally been so called in Christian liturgy. Justin Martyr wrote: "the first day after the Sabbath, remaining the first of all the days, is called, however, the eighth, according to the number of all the days of the cycle, and [yet] remains the first." A period of eight days, usually (but not always, mainly because of Christmas Day) starting and ending on a Sunday, is called an octave, particularly in Roman Catholic liturgy. In German, the phrase (literally "today in eight days") can also mean one week from today (i.e. on the same weekday). The same is true of the Italian phrase (literally "today eight") and the French . Numbering Weeks in a Gregorian calendar year can be numbered for each year. This style of numbering is often used in European and Asian countries. It is less common in the U.S. and elsewhere. The ISO week date system The system for numbering weeks is the ISO week date system, which is included in ISO 8601. This system dictates that each week begins on a Monday and is associated with the year that contains that week's Thursday. Determining Week 1 In practice week 1 (W01 in ISO notation) of any year can be determined as follows: If January 1 falls on a Monday, Tuesday, Wednesday or Thursday, then the week of January 1 is Week 1. Except in the case of January 1 falling on a Monday, this Week 1 includes the last day(s) of the previous year. If January 1 falls on a Friday, Saturday, or Sunday, then January 1 is considered to be part of the last week of the previous year. Week 1 will begin on the first Monday after January 1. Examples: Week 1 of 2015 (2015W01 in ISO notation) started