I'm researching about the latin siege of Constantinople for a project in school, and would like how much the soldiers were paid to have a basic idea of how much rough the sacking of the city was. The document Devastatio Constantinopolitana mentions the up front paying of knights and others in "marks", and in other documents "silver marks" are mentioned, I searched about the using of the word mark and the only meaning I found used in this period was a german unit of weight. Do they mean something like pounds or kilograms of silver? Were these "marks" an actual currency? If so, what country or people were they used by, and is there a way to know how much they would've been worth?
I assume that you are referring to the passage 'Interea ceperunt communia dividere, et quasi quedam preludia viginti marcas unicuique militi dare, clerico et servienti equiti decem marcas, pediti quinque marcas' from the mentioned source. In this case, your understanding is correct, as 'mark' was a common weight unit used throughout the Europe at least since high Middle Ages and customarily equal to half a pound. When used to denote the monetary value, the unit referred to half a pound of relatively pure silver. As the medieval European monetary systems usually determined the value of the currency by the number of coins minted out of a mark or a pound of silver (at least nominally, as many rulers were not above debasing the coinage by reducing the actual amount of precious metal), the purchase power of a single mark could have been easily calculated and thus marks and pounds were often used as the calculation units in larger transactions.
The exact weight and thus value of a mark was dependent on the local weight used, although given it was half a pound that was usually 400-520 grams, it could have weighed anything between 200 and 260 g with few outliers, such as Moravian or Viennese marks, both equal to roughly 280 g. For example, the Charles' pound (libra Caroli) of late 8th century was equal to roughly 408 grams and made 240 denars, while Polish mark of late 13th century was equal to 200 g and made 48 Prague groshes. In the first half of the 11th century, the Cologne Mark equal to 0.576 Charles' pound (235 grams) was introduced and popularized, so whenever the rough estimate is necessary, it makes sense to assume 235 g of silver as the equivalent of one mark anywhere in 11th-15th century (what corresponds to the period in question). Pound sterling used in England was slightly different though, as it was equal to roughly 350 grams and thus marks used after the Norman conquest in England were made equal to 2/3rds of pound sterling, roughly 235 grams, just like the aforementioned Cologne mark.
By the way, although the term 'mark' is quite common in the Western Europe, this unit was also known under a name 'grivna' in Slavic countries (pol. 'grzywna', cz. 'hřivna', rus. 'гривня**'**). On a side note, this designation is retained in the name of the modern Ukrainian currency, hryvna, much as 'mark' was the name of the currency in e.g. Germany and Finland before its replacement by euro.